Possible Anthropogenic Enhancement of Precipitation in the Sahel‐Sudan Savanna by Remote Agricultural Irrigation.

The local climatic impacts of historical expansion of irrigation are substantial, but the distant impacts are poorly understood, and their governing mechanisms generally have not been rigorously analyzed. Our experiments with an earth‐system model suggest that irrigation in the Middle East and South Asia may enhance rainfall in a large portion of the Sahel‐Sudan Savanna (SSS) to an extent comparable and opposite to its suppression by other anthropogenic climate drivers during the last several decades. The enhancement arises through a reduction in the meridional gradient of moist static energy from the Sahara Desert to the tropical rainforests. An implication of this study is that remote irrigation is a possible factor affecting the risk of drought and famine and, thus, future water security in the SSS region. Plain Language Summary: The impacts of historical expansion of agricultural irrigation on local precipitation are robust and profound, but whether irrigation can change precipitation in remote areas is poorly understood, and governing mechanisms responsible for the remote links generally have not been rigorously analyzed. Our numerical experiments with an earth‐system model suggest that irrigation in the Middle East and South Asia may enhance rainfall in a large portion of the Sahel‐Sudan Savanna (SSS). The magnitude of the enhancement is comparable to the suppression of precipitation induced by other anthropogenic climate drivers such as greenhouse emissions. The enhancement arises through a change in the large‐scale patterns of atmospheric moisture and temperature from the Sahara Desert to the tropical rainforests. Growth of remote irrigation should be considered as a possible factor affecting the risk of drought and famine in the SSS such as that experienced in the 1970s–1980s. Future regional water security in the SSS could be affected by distant water management‐groundwater depletion in South Asia and the pace of rehabilitation of war‐damaged irrigation infrastructure in the Tigris‐Euphrates valley. Key Points: Irrigation in the Middle East and South Asia may considerably enhance rainfall in the Sahel‐Sudan Savanna (SSS)The enhancement of precipitation arises through a reduction in the gradient of moist static energy from the Sahara to the tropicsThe risk and severity of drought in the SSS may be reduced by remote irrigation [ABSTRACT FROM AUTHOR]