The evolution of precipitation and warm conveyor belts during the central southwest Asia wet season

Abstract. Understanding the nature of precipitation over central southwest Asia, a data-sparse, semi-arid region, is crucial for anticipating future agricultural productivity and the likelihood of hazards such as flooding. However, the month-to-month evolution of daily precipitation characteristics, such as duration and amplitude, have not been extensively considered. Here we compare how daily precipitation and local vertical motion forcing – represented by warm conveyor belts (WCBs) – evolve from November to April over Afghanistan. Given the low amount of in-situ precipitation observations in the area, we first compare several precipitation estimates, indicating that the seasonal evolution of daily precipitation is consistent across estimates that incorporate satellite information. While these datasets agree on the timing of peak precipitation in February and March, total accumulation amounts vary substantially. Still, a common feature is that the majority of precipitation occurs on the few days when accumulation exceeds 4 mm, which are most frequent in February and March. Precipitation intensity, duration, and the associated circulation patterns evolve as winter progresses into spring, with notable differences within the months from January to April. El Niño conditions are generally associated with more heavy precipitation days than La Niña, consistent with past research, with both enhanced WCB frequency and moisture transport from lower latitudes observed during El Niño conditions, except for in January when neither precipitation nor WCB change. As such, our results support prior connections made between ENSO and seasonal-to-interannual circulation changes and extend this connection to one between the slowly-evolving ENSO influence and transient, synoptic-scale vertical motion represented by WCBs.