A Decade of Drought: Southwest Asia during the 2000s

Abstract:

Southwest Asia, which contains the nations of Iraq, Iran, Afghanistan, and Pakistan, is a water-stressed and semi-arid region that receives nearly 80 percent of its annual rainfall during November-April. The cold season climate of Southwest Asia is strongly influenced by tropical Indo-Pacific variability on intraseasonal, interannual, and decadal time scales, much of which can be attributed to sea surface temperature (SST) variations. A decade of dry conditions, and many of the driest years within the observational record since 1940, occurred during the 2000s, which resulted in adverse socioeconomic impacts, including widespread famine in the region. Here, we examine: 1) the historical context of the 2000s drought over Southwest Asia in terms of the atmospheric forcing of precipitation and their influences on soil moisture and runoff and 2) the potential predictability of future seasonal and decadal hydrologic extremes.

The synchronous SST forcing of Pacific Decadal variability in the negative phase and a warm west Pacific Ocean throughout the 2000s resulted in persistent atmospheric circulations responsible for reduced Southwest Asia precipitation. The Pacific SSTs forced anomalous anticyclonic circulation over Southwest Asia, which displaced the climatological storm track northward and interacted with the mean climate, resulting in subsidence and reduced precipitation. These atmospheric conditions over Southwest Asia were extraordinary, having never occurred for such an extended time in the observational record. During La Niña events, the aforementioned atmospheric circulations were intensified, resulting in three of the driest years since 1940.

We utilize model based soil moisture and runoff as well as observed streamflow data for analyzing 2000s drought events and examine the contribution of initial hydrologic state in seasonal scale drought predictability in this region.