Irrigation-induced land-atmosphere feedbacks and their impacts on Indian summer monsoon
Journal
Journal of Climate
Journal Volume
31
Journal Issue
21
Pages
8785-8801
Date Issued
2018
Author(s)
Abstract
From the 1980s, Indian summer monsoon rainfall (ISMR) shows a decreasing trend over north and northwest India, and there was a significant observed reduction in July over central and south India in 1982-2003. The key drivers of the changed ISMR, however, remain unclear. It was hypothesized that the large-scale irrigation development that started in the 1950s has resulted in land surface cooling, which slowed large-scale atmospheric circulation, exerting significant influences on ISMR. To test this hypothesis, a fully coupled model, the CESM v1.0.3, was used with a global irrigation dataset. In this study, spatially varying irrigation-induced feedback mechanisms are investigated in detail at different stages of the monsoon. Results show that soil moisture and evapotranspiration increase significantly over India throughout the summertime because of the irrigation. However, 2-m air temperature shows a significant reduction only in a limited region because the temperature change is influenced simultaneously by surface incoming shortwave radiation and evaporative cooling resulting from the irrigation, especially over the heavily irrigated region. Irrigation also induces a 925-hPa northeasterly wind from 30°N toward the equator. This is opposite to the prevailing direction of the Indian summer monsoon (ISM) wind that brings moist air to India. The modeled rainfall in the irrigated case significantly decreases up to 1.5 mm day-1 over central and north India from July to September. This paper reveals that the irrigation can contribute to both increasing and decreasing the surface temperature via multiple feedback mechanisms. The net effect is to weaken the ISM with the high spatial and temporal heterogeneity. © 2018 American Meteorological Society.
Subjects
Atmosphere-land interaction; Hydrology
Other Subjects
Atmospheric thermodynamics; Evaporative cooling systems; Evapotranspiration; Feedback control; Hydrology; Rain; Soil moisture; Statistical tests; Atmosphere-land interactions; Atmospheric circulation; Indian summer monsoon; Indian summer monsoon rainfall; Irrigation development; Short-wave radiation; Spatial and temporal heterogeneity; Surface temperatures; Irrigation; air-soil interaction; climate feedback; evapotranspiration; hydrology; irrigation; monsoon; rainfall; soil moisture; summer; India
Type
journal article