Simulation of vegetation net primary productivity and evapotranspiration based on LPJ model in Central Asia

Central Asia is one of the most sensitive regions to climate changes in the world and the ecological environment is very fragile. The two main vegetation types, grasslands and croplands, are very easily influenced by water shortages and humans activities. Study on changes of net primary productivity (NPP) and evapotranspiration(ET), and their relationship with climate are important in Central Asia. In the present study, the spatio-temporal patterns and changes of NPP and ET in Central Asia (1982-2012) were analyzed based on LPJ model. The results indicated that the spatial distributions of NPP and ET were very consistent. The high-values were mainly located in forests, the mixed area of grass-forest and croplands, whereas the low-values were mainly concentrated in sparse vegetated area around the desert and grasslands of central Kazakhstan. The annual NPP and ET showed a fluctuated increasing trend. Annual NPP varied from 469.59 Tg C·a-1 to 1 130.26 Tg C·a-1 with mean of 737.24 Tg C·a-1(185.57 g C·m-2·a-1). Annual ET varied from 695.53 km3·a-1 to 1 047.69 km3·a-1 with mean of 850.46 km3·a-1 (214.07 mm·a-1). The main climate factor influencing the variations of NPP and ET was precipitation in Central Asia, while temperature played less important role in the region. The vegetation productivity of Kyrgyzstan and Tajikistan increased at a faster rate, yet Turkmenistan indicated a decline trend. Kazakhstan, Uzbekistan and Xinjiang’s vegetation productivitywere relatively stable.