Characteristics, Precursors, and Predictability of Amu Darya Drought

The socioeconomic stability of the Central Asian Republics in the Amu Darya watershed is sensitive drought, given that activities related to agriculture employ a large fraction of the population and are responsible for at least one fifth of the gross domestic products of Afghanistan, Tajikistan and Turkmenistan. Toward building a predictive understanding that may be applied to drought and famine early warning practices, the characteristics, precursors and predictability of agricultural drought over the Amu Darya watershed are examined in a large ensemble of fully coupled earth system model simulations during 1920-2019. Agricultural drought is examined over Upper and Lower regions of the Amu Darya watershed, which have different mean hydroclimates, and is defined by 1-m soil moisture deficits lasting three or more months.

The risk of drought onset and demise follows the precipitation seasonality of each region and is closely related to the El Niño Southern Oscillation (ENSO). For the Upper region, the risk of drought onset and demise is three times more likely to occur during the fall and spring than other seasons. For the Lower region, the risk of drought onset and demise is three times more likely to occur during November-April than the warm season. Drought onset and demise for both regions are closely related to precipitation deficits and surpluses, respectively, during the target month and month prior, though it is possible for them to occur within one month. The risk of drought onset and demise are closely related to La Niña and El Niño, respectively, thereby indicating that the ENSO state serves as a key predictor of drought phase changes.

Natural climate variations are responsible for the behavior of key agricultural drought characteristics over the Amu Darya watershed, given that the model simulations suggest no long-term changes in 1-m soil moisture due to anthropogenic influences. The prevalence of drought over epochs of given lengths can be highly variable. For both the Upper and Lower Amu Darya, the regions can spend as little as 10 years or as many as 40 years in drought in a 100-year period. The length of individual droughts is also highly variable. 50 percent of droughts last less than six months and 12 months over the Upper and Lower regions, respectively. However, droughts can last up to five years and eight years over the Upper and Lower regions, respectively.

Amu Darya watershed drought is related to droughts across the globe though links to La Niña events. Amu Darya drought during the cold season is related to drought over the southern tier of the United States, the Horn of Africa and Indonesia and pluvial conditions over the eastern Sahel, Australia, southeast Asia and Brazil. Amu Darya drought during the warm season is not as closely related to global droughts, given that Amu Darya summertime conditions are not as closely related to ENSO.