Assessment of drought frequency, duration, and severity and its impact on pasture production in Mongolia

Drought frequency, duration, and severity and its impact on pasture productivity in the four main vegetation zones of Mongolia were analyzed using meteorological, soil moisture, and vegetation data during the growing season (April-August) of 1965-2010. Meteorological and pasture drought characteristics were explored using the Standardized Precipitation Index (SPI), the soil moisture anomalies percentile index (W (p)), and Palmer Drought Severity Index (PDSI) on 1-month timescale. Generally, 35-37 (15-16 %) by SPI for meteorological drought while 27-29 (12-13 %) by W (p), and 16-21 (7-9 %) by PDSI for pasture drought with different durations were identified over the four vegetation zones during the study period. Most of these droughts (80 % by SPI and 50-60 % by both W (p) and PDSI) observed during the entire events occurred on a 1-month duration with moderate intensity. Drought frequencies were not significantly (p > 0.05) different within the four zones. The frequency of the short-term meteorological droughts was observed relatively greater than pasture droughts; however, pasture droughts were more persistent and severe than meteorological droughts. The three indices show that the frequency and severity of droughts have slightly increased over the 46 years with significant (p < 0.05) dry conditions during the last decade of 2001-2010 in the four zones (except in the high mountain). The results showed the W (p) was more highly significantly correlated with the precipitation anomalies (r = 0.68) and pasture production (r = 0.55) than PDSI (r = 0.51, p < 0.05 and r = 0.38, p < 0.10, respectively). A statistical model, based on pasture production and the W (p), suggested that the consecutive drought months contribution during the growing season was 30 % (p < 0.05) and that pasture production was more sensitive to the occurrence of droughts during June-August (R (2) = 0.32, p < 0.05) as seen in 2000-2002 and 2007. We concluded that a greater severity and frequency of growing-season droughts, during the last decade of 2001-2010, have driven a reduction in pasture production in Mongolia.