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- Title
The Role of Irrigation Expansion on Historical Climate Change: Insights From CMIP6.
- Authors
Al‐Yaari, A.; Ducharne, A.; Thiery, W.; Cheruy, F.; Lawrence, D.
- Abstract
To produce food for a growing world population, irrigated areas have increased from approximately 0.63 million km2 of land in 1900 to 3.1 million km2 of land in 2005. Despite this massive expansion, irrigation is still overlooked in most state‐of‐the‐art Earth system models (ESMs) involved in the Coupled Model Intercomparison Project phase 6 (CMIP6). To our knowledge, only three CMIP6 models represent irrigation activities: CESM2, GISS‐E2‐1‐G, and NorESM2‐LM. Here, we investigate the role of irrigation on historical climate at global and regional scales by analyzing trends of key surface climate variables in CMIP6 simulations during 1900–2014. The three models including irrigation show distinct behavior from the 15 models without irrigation over intensively irrigated areas (i.e., >50% of grid cell area is equipped by irrigation): both annual (months that correspond to monthly air temperature higher than 274 K) mean latent heat flux (LHF) and soil moisture increase over time, in contrast to the models without irrigation that show no trend or even a negative trend. The positive LHF trend over intensively irrigated areas in the irrigation‐on models is consistent with three satellite‐based LHF products. While annual (considering the warmest month in a year) warming trends are found in these regions for most of the no‐irrigation models, the increase in LHF induces a cooling trend for the models with irrigation, which was not confirmed by observational air temperature data sets. These findings, supported by satellite data, indicate the importance of improved representation of land management in the next generation of ESM. Plain Language Summary: Expansion of irrigated areas influences long‐term terrestrial water and energy cycles, primarily via enhanced evapotranspiration from irrigated surfaces. Here, we analyze long‐term (1900–2014) trends of latent heat flux (LHF), soil moisture, precipitation, net radiation, and air temperature from the latest generation of Earth system models (ESMs) involved in the Coupled Model Intercomparison Project phase 6 (CMIP6). Only three CMIP6 models account for irrigation activities, while all others omit irrigation. Based on the trend results, a distinct behavior of the three models is observed, with the annual mean LHF and soil moisture generally increasing over heavily irrigated regions, with a corresponding cooling trend in the annual maximum of monthly air temperature. We find that neglecting irrigation reduces the accuracy of LHF trend estimates over heavily irrigated regions, as the performance of models without irrigation was poor when compared to observation‐based data sets. Our study overall highlights the importance of irrigation as a historical climate forcing and underlines the benefit of incorporating irrigation in the next generation of ESM to reduce uncertainties in historical climate simulations and enhance the reliability of future projections. Key Points: Trends of six essential climate variables were compared between Coupled Model Intercomparison Project phase 6 (CMIP6) simulations with (CMIP6.irr) and without (CMIP6.noirr) irrigationCMIP6.irr exhibits a distinct behavior in better capturing the upward trend of observed latent heat flux over heavily irrigated regionsOver the same regions, while CMIP6.irr exhibits a cooling trend, CMIP6.noirr exhibits a warming trend
- Subjects
IRRIGATION; CLIMATE change; LATENT heat; HEAT flux; GRID cells; GLOBAL cooling
- Publication
Earth's Future, 2022, Vol 10, Issue 11, p1
- ISSN
2328-4277
- Publication type
Article
- DOI
10.1029/2022EF002859