Applying the Moisture Availability Index (NTDI) over Vegetated Land in Central Asia: Mongolian Steppe

Abstract

The intensity of recent droughts and the uncertainty of moisture variability in the context of increasing temperatures and decreasing precipitation have affected the Mongolian grassland. Mongolia typifies the steppe terrain and semiarid to arid continental climate that extends across much of Central Asia. In semi-arid areas like Mongolian steppe, vegetation type and distribution are directly relate to the amount of water that plants can extract from the soil. An index for assessment of moisture availability (<i>m</i>_a: defined as the ratio of actual to reference evapotranspiration) was developed, namely NTDI [1] 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003400300031003800340037003500380031000000 . NTDI (Normalized Day-Night Surface Temperature Difference Index) is defined as the ratio of the difference between the maximum daytime surface temperature and the minimum nighttime surface temperature, to the difference between the maximum and minimum surface temperatures estimated from meteorological data by applying energy balance equations. A verification study conducted at Liudaogou River Basin of the Loess Plateau, China, indicated the capability of NTDI to estimate <i>m</i>_a accurately, ( R 2 =0.97,p<0.001) [1] 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003400300031003800340037003500380031000000 . In Bayan Unjuul, Mongolia, application of NTDI during the growing season showed a significant inverse exponential correlation with <i>m</i>_a ( R 2 =0.86,p<0.001). This result indicates that the NTDI is potent to be used as a surrogate of moisture availability in steppe terrain of Central Asia.