AGW Observer

Observations of anthropogenic global warming

Papers on irrigation and climate

Posted by Ari Jokimäki on September 2, 2010

This is a list of papers on the irrigation effects to climate. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Effects of irrigation on global climate during the 20th century – Puma & Cook (2010) “Various studies have documented the effects of modern-day irrigation on regional and global climate, but none, to date, have considered the time-varying impact of steadily increasing irrigation rates on climate during the 20th century. We investigate the impacts of observed irrigation changes over this century with two ensemble simulations using an atmosphere general circulation model. Both ensembles are forced with transient climate forcings and observed sea surface temperatures from 1902 to 2000; one ensemble includes irrigation specified by a time-varying data set of irrigation water withdrawals. Early in the century, irrigation is primarily localized over southern and eastern Asia, leading to significant cooling in boreal summer (June–August) over these regions. This cooling spreads and intensifies by century’s end, following the rapid expansion of irrigation over North America, Europe, and Asia. Irrigation also leads to boreal winter (December–February) warming over parts of North America and Asia in the latter part of the century, due to enhanced downward longwave fluxes from increased near-surface humidity. Precipitation increases occur primarily downwind of the major irrigation areas, although precipitation in parts of India decreases due to a weaker summer monsoon. Irrigation begins to significantly reduce temperatures and temperature trends during boreal summer over the Northern Hemisphere midlatitudes and tropics beginning around 1950; significant increases in precipitation occur in these same latitude bands. These trends reveal the varying importance of irrigation-climate interactions and suggest that future climate studies should account for irrigation, especially in regions with unsustainable irrigation resources.” Puma, M. J., and B. I. Cook (2010), J. Geophys. Res., 115, D16120, doi:10.1029/2010JD014122. [Full text]

Effects of global irrigation on the near-surface climate – Sacks et al. (2009) “Irrigation delivers about 2,600 km3 of water to the land surface each year, or about 2% of annual precipitation over land. We investigated how this redistribution of water affects the global climate, focusing on its effects on near-surface temperatures. Using the Community Atmosphere Model (CAM) coupled to the Community Land Model (CLM), we compared global simulations with and without irrigation. To approximate actual irrigation amounts and locations as closely as possible, we used national-level census data of agricultural water withdrawals, disaggregated with maps of croplands, areas equipped for irrigation, and climatic water deficits. We further investigated the sensitivity of our results to the timing and spatial extent of irrigation. We found that irrigation alters climate significantly in some regions, but has a negligible effect on global-average near-surface temperatures. Irrigation cooled the northern mid-latitudes; the central and southeast United States, portions of southeast China and portions of southern and southeast Asia cooled by ~0.5 K averaged over the year. Much of northern Canada, on the other hand, warmed by ~1 K. The cooling effect of irrigation seemed to be dominated by indirect effects like an increase in cloud cover, rather than by direct evaporative cooling. The regional effects of irrigation were as large as those seen in previous studies of land cover change, showing that changes in land management can be as important as changes in land cover in terms of their climatic effects. Our results were sensitive to the area of irrigation, but were insensitive to the details of irrigation timing and delivery.” William J. Sacks, Benjamin I. Cook, Nikolaus Buenning, Samuel Levis and Joseph H. Helkowski, Climate Dynamics, Volume 33, Numbers 2-3, 159-175, DOI: 10.1007/s00382-008-0445-z. [Full text]

The impact of agricultural intensification and irrigation on land–atmosphere interactions and Indian monsoon precipitation — A mesoscale modeling perspective – Douglas et al. (2009) “Using the Regional Atmospheric Modeling System (RAMS) we show that agricultural intensification and irrigation can modify the surface moisture and energy distribution, which alters the boundary layer and regional convergence, mesoscale convection, and precipitation patterns over the Indian monsoon region. Four experiments were conducted to simulate a rain event from 16 to 20 July 2002 over the Indian region: (i) a control with Global Land Cover land use and observed Normalized Difference Vegetation Index, (ii) an irrigated crop scenario, (iii) a non-irrigated crop scenario, and (iv) a scenario for potential (natural) vegetation. Results indicate that even under active monsoon conditions, the simulated surface energy and moisture flux over the Indian monsoon region are sensitive to the irrigation intensity and this effect is more pronounced than the impact of land use change from the potential vegetation to the agricultural landscape. When model outputs were averaged over the south Asia model domain, a statistically significant decrease in mean sensible heat flux between the potential vegetation and the irrigated agriculture scenarios of 11.7 Wm− 2 was found. Changes in latent heat fluxes ranging from − 20.6 to + 37.2 Wm− 2 (− 26% to + 24%) and sensible heat fluxes ranging − 87.5 to + 4.4 Wm− 2 (− 77% to + 8%) fluxes were found when model outputs were averaged over Indian states. Decreases in sensible heat in the states of Punjab (87.5 Wm− 2 or 77%) and Haryana (65.3 Wm− 2 or 85%) were found to be statistically significant at the 95% confidence level. Irrigation increased the regional moisture flux which in turn modified the convective available potential energy. This caused a reduction in the surface temperature and led to a modified regional circulation pattern and changes in mesoscale precipitation. These agricultural changes, including irrigation modify the mesoscale convection and rain patterns in the Indian monsoon region. These regional changes in land use need to be considered in improved weather forecasting as well as multi-decadal climate variability and change assessments.” E.M. Douglas, A. Beltrán-Przekurat, D. Niyogi, R.A. Pielke Sr. and C.J. Vörösmarty, Global and Planetary Change, Volume 67, Issues 1-2, May 2009, Pages 117-128, doi:10.1016/j.gloplacha.2008.12.007. [Full text]

Impact of irrigation on the South Asian summer monsoon – Saeed et al. (2009) “The Indian subcontinent is one of the most intensely irrigated regions of the world and state of the art climate models do not account for the representation of irrigation. Sensitivity studies with the regional climate model REMO show distinct feedbacks between the simulation of the monsoon circulation with and without irrigation processes. We find that the temperature and mean sea level pressure, where the standard REMO version without irrigation shows a significant bias over the areas of Indus basin, is highly sensitive to the water used for irrigation. In our sensitivity test we find that removal of this bias has caused less differential heating between land and sea masses. This in turns reduces the westerlies entering into land from Arabian Sea, hence creating conditions favorable for currents from Bay of Bengal to intrude deep into western India and Pakistan that have been unrealistically suppressed before. We conclude that the representation of irrigated water is unavoidable for realistic simulation of south Asian summer monsoon and its response under global warming.” Saeed, F., S. Hagemann, and D. Jacob (2009), Geophys. Res. Lett., 36, L20711, doi:10.1029/2009GL040625.

Regional Differences in the Influence of Irrigation on Climate – Lobell et al. (2009) “A global climate model experiment is performed to evaluate the effect of irrigation on temperatures in several major irrigated regions of the world. The Community Atmosphere Model, version 3.3, was modified to represent irrigation for the fraction of each grid cell equipped for irrigation according to datasets from the Food and Agriculture Organization. Results indicate substantial regional differences in the magnitude of irrigation-induced cooling, which are attributed to three primary factors: differences in extent of the irrigated area, differences in the simulated soil moisture for the control simulation (without irrigation), and the nature of cloud response to irrigation. The last factor appeared especially important for the dry season in India, although further analysis with other models and observations are needed to verify this feedback. Comparison with observed temperatures revealed substantially lower biases in several regions for the simulation with irrigation than for the control, suggesting that the lack of irrigation may be an important component of temperature bias in this model or that irrigation compensates for other biases. The results of this study should help to translate the results from past regional efforts, which have largely focused on the United States, to regions in the developing world that in many cases continue to experience significant expansion of irrigated land.” Lobell, David, Govindasamy Bala, Art Mirin, Thomas Phillips, Reed Maxwell, Doug Rotman, 2009: Regional Differences in the Influence of Irrigation on Climate. J. Climate, 22, 2248–2255, doi: 10.1175/2008JCLI2703.1. [Full text]

Effects of irrigation and vegetation activity on early Indian summer monsoon variability – Lee et al. (2009) “We examined the effects of land cover change over the Indian subcontinent during pre-monsoon season (March, April, and May—MAM) on early Indian summer monsoon (ISM) rainfall using observed Normalized Difference Vegetation Index (NDVI) and July precipitation for the period of 1982–2003. MAM NDVI anomalies have increased in the Indian subcontinent and the increases are significantly correlated with increases in the irrigated area, not preceding rainfall. July rainfall significantly decreased in central and southern India, and the decrease is statistically related to the increase in the preceding MAM NDVI anomalies. Decreased July surface temperature in the Indian subcontinent (an expected result of increased evapotranspiration due to irrigation and increased vegetation) leads to a reduced land–sea thermal contrast, which is one of the factors driving the monsoon, and therefore weakens the monsoon circulation. A weak early ISM appears to be at least partially a result of irrigation and the resultant increased vegetation and crop activity prior to the monsoon.” Eungul Lee, Thomas N. Chase, Balaji Rajagopalan, Roger G. Barry, Trent W. Biggs, Peter J. Lawrence, International Journal of Climatology, Volume 29, Issue 4, pages 573–581, 30 March 2009, DOI: 10.1002/joc.1721. [Full text]

The Role of Irrigation Expansion in Past and Future Temperature Trends – Lobell et al. (2008) “Expansion of irrigated land can cause local cooling of daytime temperatures by up to several degrees Celsius. Here the authors compare the expected cooling associated with rates of irrigation expansion in developing countries for historical (1961–2000) and future (2000–30) periods with climate model predictions of temperature changes from other forcings, most notably increased atmospheric greenhouse gas levels, over the same periods. Indirect effects of irrigation on climate, via methane production in paddy rice systems, were not considered. In regions of rapid irrigation growth over the past 40 yr, such as northwestern India and northeastern China, irrigation’s expected cooling effects have been similar in magnitude to climate model predictions of warming from greenhouse gases. A masking effect of irrigation can therefore explain the lack of significant increases in observed growing season maximum temperatures in these regions and the apparent discrepancy between observations and climate model simulations. Projections of irrigation for 2000–30 indicate a slowing of expansion rates, and therefore cooling from irrigation expansion over this time period will very likely be smaller than in recent decades. At the same time, warming from greenhouse gases will likely accelerate, and irrigation will play a relatively smaller role in agricultural climate trends. In many irrigated regions, therefore, temperature projections from climate models, which generally ignore irrigation, may be more accurate in predicting future temperature trends than their performance in reproducing past observed trends in irrigated regions would suggest.” Lobell, David B., Céline Bonfils, Jean-Marc Faurès, 2008, Earth Interact., 12, 1–11, doi: 10.1175/2007EI241.1.

The Effect of Irrigation on Regional Temperatures: A Spatial and Temporal Analysis of Trends in California, 1934–2002 – Lobell & Bonfils (2008) “The response of air temperatures to widespread irrigation may represent an important component of past and/or future regional climate changes. The quantitative impact of irrigation on daily minimum and maximum temperatures (Tmin and Tmax) in California was estimated using historical time series of county irrigated areas from agricultural censuses and daily climate observations from the U.S. Historical Climatology Network. Regression analysis of temperature and irrigation changes for stations within irrigated areas revealed a highly significant (p < 0.01) effect of irrigation on June–August average Tmax, with no significant effects on Tmin (p > 0.3). The mean estimate for Tmax was a substantial 5.0°C cooling for 100% irrigation cover, with a 95% confidence interval of 2.0°–7.9°C. As a result of small changes in Tmin compared to Tmax, the diurnal temperature range (DTR) decreased significantly in both spring and summer months. Effects on percentiles of Tmax within summer months were not statistically distinguishable, suggesting that irrigation’s impact is similar on warm and cool days in California. Finally, average trends for stations within irrigated areas were compared to those from nonirrigated stations to evaluate the robustness of conclusions from previous studies based on pairwise comparisons of irrigated and nonirrigated sites. Stronger negative Tmax trends in irrigated sites were consistent with the inferred effects of irrigation on Tmax. However, Tmin trends were significantly more positive for nonirrigated sites despite the apparent lack of effects of irrigation on Tmin from the analysis within irrigated sites. Together with evidence of increases in urban areas near nonirrigated sites, this finding indicates an important effect of urbanization on Tmin in California that had previously been attributed to irrigation. The results therefore demonstrate that simple pairwise comparisons between stations in a complex region such as California can lead to misinterpretation of historical climate trends and the effects of land use changes.” Lobell, David B., Céline Bonfils, 2008, J. Climate, 21, 2063–2071, doi: 10.1175/2007JCLI1755.1. [Full text]

Empirical evidence for a recent slowdown in irrigation-induced cooling – Bonfils & Lobell (2007) “Understanding the influence of past land use changes on climate is needed to improve regional projections of future climate change and inform debates about the tradeoffs associated with land use decisions. The effects of rapid expansion of irrigated area in the 20th century has remained unclear relative to other land use changes, such as urbanization, that affected a similar total land area. Using spatial and temporal variations in temperature and irrigation extent observed in California, we show that irrigation expansion has had a large cooling effect on summertime average daily daytime temperatures (−0.14°C to −0.25°C per decade), which corresponds to an estimated cooling of −1.8°C to −3.2°C since the introduction of irrigation practices. Irrigation has negligible effects on nighttime temperatures, leading to a net cooling effect of irrigation on climate (−0.06°C to −0.19°C per decade). Stabilization of irrigated area has occurred in California since 1980 and is expected in the near future for many irrigated regions. The suppression of past human-induced greenhouse warming by increased irrigation is therefore likely to slow in the future, and a potential decrease in irrigation may even contribute to a more rapid warming. Changes in irrigation alone are not expected to influence broad-scale temperatures, but they may introduce large uncertainties in climate projections for irrigated agricultural regions, which provide ≈40% of global food production.” Céline Bonfils and David Lobell, PNAS August 21, 2007 vol. 104 no. 34 13582-13587, doi: 10.1073/pnas.0700144104. [Full text]

Irrigation cooling effect: Regional climate forcing by land-use change – Kueppers et al. (2007) “Regional detection of a greenhouse warming signal relies on extensive, long-term measurements of temperature. The potentially confounding impact of land-cover and land-use change on trends in temperature records has mostly focused on the influence of urban heat islands. Here we use a regional climate model to show that a regional irrigation cooling effect (ICE) exists, opposite in sign to urban heat island effects. The magnitude of the ICE has strong seasonal variability, causing large dry-season decreases in monthly mean and maximum temperatures, but little change in rainy-season temperatures. Our model produced a negligible effect on monthly minimum temperature. In California, the modeled regional ICE is of similar magnitude, but opposite sign, to predictions for future regional warming from greenhouse gases. Given our results for California and the global importance of irrigated agriculture, past expansion of irrigated land has likely affected observations of surface temperature, potentially masking the full warming signal caused by greenhouse gas increases.” Kueppers, L. M., M. A. Snyder, and L. C. Sloan (2007), Geophys. Res. Lett., 34, L03703, doi:10.1029/2006GL028679.

Effects of irrigation on the water and energy balances of the Colorado and Mekong river basins – Haddeland et al. (2006) “An irrigation scheme, based on simulated soil moisture deficit, has been included in the variable infiltration capacity macroscale hydrologic model. Water withdrawals are taken from the nearest river, or, in periods of water scarcity, from reservoirs. Alternatively, water can be assumed freely available. The irrigation scheme successfully simulates crop consumptive water use in large river basins. In general, irrigation leads to decreased streamflow and increased evapotranspiration. The locally significant increases in evapotranspiration (or latent heat) results in lower surface temperatures, and hence decreased sensible heat flux. Simulations performed for a 20-year period for the Colorado and Mekong river basins indicate irrigation water requirements of 10 and 13.4 km3 year−1, respectively, corresponding to streamflow decreases of 37 and 2.3%. The increase in latent heat flux is accompanied by a decrease in annual averaged surface temperatures of 0.04 °C for both river basins. The maximum simulated increase in latent heat flux averaged over the three peak irrigation months for one grid cell is 63 W m−2, where surface temperature decreases 2.1 °C. Simulated actual water use is somewhat less than simulated irrigation water requirements; 8.3 and 12.4 km3 year−1 for the Colorado and Mekong river basin, respectively.” Ingjerd Haddeland, Dennis P. Lettenmaier, and Thomas Skaugen, Journal of Hydrology, Volume 324, Issues 1-4, 15 June 2006, Pages 210-223, doi:10.1016/j.jhydrol.2005.09.028.

Direct human influence of irrigation on atmospheric water vapour and climate – Boucher et al. (2004) “Human activity increases the atmospheric water vapour content in an indirect way through climate feedbacks. We conclude here that human activity also has a direct influence on the water vapour concentration through irrigation. In idealised simulations we estimate a global mean radiative forcing in the range of 0.03 to +0.1 Wm–2 due to the increase in water vapour from irrigation. However, because the water cycle is embodied in the climate system, irrigation has a more complex influence on climate. We also simulate a change in the temperature vertical profile and a large surface cooling of up to 0.8 K over irrigated land areas. This is of opposite sign than expected from the radiative forcing alone, and this questions the applicability of the radiative forcing concept for such a climatic perturbation. Further, this study shows stronger links than previously recognised between climate change and freshwater scarcity which are environmental issues of paramount importance for the twenty first century.” O. Boucher, G. Myhre and A. Myhre, Climate Dynamics, Volume 22, Numbers 6-7, 597-603, DOI: 10.1007/s00382-004-0402-4. [Full text]

Impact of Irrigation on Midsummer Surface Fluxes and Temperature under Dry Synoptic Conditions: A Regional Atmospheric Model Study of the U.S. High Plains – Adegoke et al. (2003) “The impact of irrigation on the surface energy budget in the U.S. high plains is investigated. Four 15-day simulations were conducted: one using a 1997 satellite-derived estimate of farmland acreage under irrigation in Nebraska (control run), two using the Olson Global Ecosystem (OGE) vegetation dataset (OGE wet run and OGE dry run), and the fourth with the Kuchler vegetation dataset (natural vegetation run) as lower boundary conditions in the Colorado State University Regional Atmospheric Modeling System (RAMS). In the control and OGE wet simulations, the topsoil in the irrigated locations, up to a depth of 0.2 m, was saturated at 0000 UTC each day for the duration of the experiment (1–15 July 1997). In the other two runs, the soil was allowed to dry out, except when replenished naturally by rainfall. Identical observed atmospheric conditions were used along the lateral boundary in all four cases. The area-averaged model-derived quantities for the grid centered over Nebraska indicate significant differences in the surface energy fluxes between the control (irrigated) and the “dry” simulations. For example, a 36% increase in the surface latent heat flux and a 2.6°C elevation in dewpoint temperature between the control run and the OGE dry run is shown. Surface sensible heat flux of the control run was 15% less and the near-ground temperature was 1.2°C less compared to the OGE dry run. The differences between the control run and the natural vegetation run were similar but amplified compared to the control run–OGE dry run comparisons. Results of statistical analyses of long-term (1921–2000) surface temperature data from two sites representing locations of extensive irrigated and nonirrigated land uses appear to support model results presented herein of an irrigation-related cooling in surface temperature. Growing season monthly mean and monthly mean maximum temperature data for the irrigated site indicate a steady decreasing trend in contrast to an increasing trend at the nonirrigated site.” Adegoke, Jimmy O., Roger A. Pielke, J. Eastman, Rezaul Mahmood, Kenneth G. Hubbard, 2003, Mon. Wea. Rev., 131, 556–564. [Full text]

Irrigation-Induced Rainfall and the Great Plains – Moore & Rojstaczer (2001) “The post–World War II increase in irrigation in the Great Plains represents the largest human-induced hydrologic impact in North America. Drawn primarily from the High Plains aquifer, water applied as irrigation in the region amounts to billions of cubic meters (2 × 1010 m3 in 1990) annually and is applied to more than 60 000 km2 of farmland. Following studies by Schickedanz and by Barnston and Schickedanz, empirical orthogonal functions and precipitation magnitude comparisons were employed to examine trends in precipitation over the region and to determine if this enormous addition of irrigation water to the surface has had a measurable influence on precipitation during the summer months of June, July, and August. The Barnston and Schickedanz study observed a transition from unirrigated to heavily irrigated conditions; in contrast, this examination focused on a more recent period during which irrigation took place throughout the time of interest. Loading patterns and temporal precipitation trends for 1950–97 show, at best, slight evidence that irrigation induces rainfall. The most prominent evidence of an irrigation effect is found in the Texas Panhandle for 1950–82. If irrigation-induced rainfall exists, its impact is only minor relative to the natural determining factors of plains climate. It also is possible that the chief influence of irrigation on rainfall may take place at some threshold magnitude of irrigation (not explored in this study) that already had been exceeded by 1950.” Moore, Nathan, Stuart Rojstaczer, 2001, J. Appl. Meteor., 40, 1297–1309, doi: 10.1175/1520-0450(2001)0402.0.CO;2. [Full text]

On the Potential Impact of Irrigated Areas in North America on Summer Rainfall Caused by Large-Scale Systems – Segal et al. (1998) “The potential impact of the increase in irrigated areas in North America during the past 100 years on summer rainfall associated with medium- to large-scale precipitation systems is evaluated conceptually and by several illustrative numerical model simulations. The model results for the simulated cases suggest a tendency toward some increase in the continental-average rainfall for the present irrigation conditions compared with those of past irrigation. The maximum increase obtained for several studied cases of 6-day duration each was 1.7%. Rainfall increases typically occur in the location of existing rainfall areas, and the main effect of irrigation is to redistribute rainfall in those preexisting precipitation regions.” Segal, M., Z. Pan, R. W. Turner, E. S. Takle, 1998, J. Appl. Meteor., 37, 325–331, doi: 10.1175/1520-0450-37.3.325. [Full text]

The Effect of Irrigation on Premonsoon Season Precipitation over South West Bengal, India – Lohar & Pal (1995) “The present work is on the modification of climatic variables, such as rainfall, as a result of change in land use during the premonsoon period over the southern part of West Bengal, India. Data analysis supports a decreasing tendency in rainfall during the recent years. As a possible factor behind such change, a significant increase in agricultural activity during recent years in coastal and inland regions has been stressed. The increase in soil moisture as a result of irrigation hinders the development and intensity of the sea-breeze circulation. The low-level moisture supply also decreases, which is an essential criterion for the formation of premonsoon thunderstorms, that is, northwesters. So, the increased vegetation or soil moisture is not always likely to increase rainfall activity; rather, mesoscale effects may be more important in some specific areas.” Lohar, D., B. Pal, 1995, J. Climate, 8, 2567–2570. [Full text]

The Effect of Irrigation on Warm Season Precipitation in the Southern Great Plains – Barnston & Schickedanz (1984) “The synoptic and subsynoptic atmospheric processes that accompany statistically determined periods of irrigation-induced rainfall increases during the warm season in the Texas Panhandle are examined. Major results are as follows. Irrigation appears to increase precipitation only when the synoptic condition provides low-level convergence and uplift, such that the additional moisture produced by irrigation (normally confined to the lowest 10–20 m of the atmosphere) is allowed to ascend to cloud base. Stationary fronts are the most favorable such synoptic condition because they fulfill the requirement for longer time durations than moving fronts or surface low pressure centers. The effect of irrigation is more noticeable during generally rainy periods because such periods often contain the types of significant rainfall events that provide sustained low-level convergence over the irrigated region. Because the mean storm track is closer to north Texas in June than in July and August, the irrigation-produced rainfall anomaly in June (which often is >20% in and somewhat downwind of the irrigation core) is the greatest of these three heavily irrigated months. Irrigation appears to lower the daily surface maximum temperature by 2°C during dry, hot conditions and by 1°C on damp, cooler days. When combining the temperature anomalies with known increases in surface dewpoint, the lifted index is estimated to decrease by up to 1°C, slightly increasing the probability of convection, even in the absence of convergence. Other possible mesoscale effects of irrigation are discussed.” Barnston, Anthony G., Paul T. Schickedanz, 1984, J. Climate Appl. Meteor., 23, 865–888. [Full text]

The Effect of Irrigation on Precipitation in the Great Plains – Schickedanz (1976) “This research addressed the question of whether the extensive irrigation in the Great Plains has had an appreciable effect on the climate of the region. The primary objectives of the research were to examine for a rainfall anomaly due to irrigation and to measure the magnitude of the effect. Another objective was to investigate other associated weather variables for supportive relationships which also could be used to help explain the physical causes. The basic study region included the states of Kansas, Nebraska, and a large portion of the state of Texas. In addition, some data rom the states of Colorado, New Mexico, Wyoming, Iowa, Missouri, and South Dakota were used for extra-area control purposes. The analysis of rainfall trend maps , the factor analysis, the analysis of convariance, and the ratio comparison patterns produced strong evidence for irrigation effects in Nebraska during June, in Texas and Kansas during July, in Kansas during August, and in all three states during summer, (Sims-ISWS).” Schickedanz, PT, 1976, Available from the National Technical Information Service, Springfield VA 22161 as PB-264 921, Report No. NSF/RA-760460, November 1976, 111 p, 29 fig, 9 tab, 30 ref. NSF GI-43871.

The influence of irrigation on the energy balance and the climate near the ground – de Vries (1959) “A theoretical analysis is presented of the influence of irrigation on temperature and humidity of the lower air layers and on the energy balance of the surface. Starting from meteorological data for the dry land (averaged over periods of a few days or longer), the average temperature and moisture profiles in an irrigated area are calculated as functions of the distance downwind from its boundary. The principal simplifying assumption in the analysis is that for each height the eddy diffusivities should have the same values in the irrigated and non-irrigated areas. The theory is applied to and illustrated by measurements of climatic differences between irrigated and non-irrigated pastures in the Australian Riverina. Experimental results of other investigators are briefly discussed. The present developments have led to a theoretical estimate, taking advective energy into account, of the potential evaporation rate for irrigated areas of limited extent on the basis of standard meteorological data for the dry land. The influence of advection decreases rapidly with increasing distance downwind. Under summer conditions in the Australian Riverina, it is considerable up to distances of about 1 km.” de Vries, D. A., 1959, J. Meteor., 16, 256–270. [Full text]

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