# The Net Influence of Drought on Grassland Productivity over the Past 50 Years
## 3 Results and Discussion
### The Interaction of Precipitation and Temperature on Grassland Productivity
In most cases, the climatic patterns of the 20 th century have contributed to the growth of forest ecosystem productivity [44]. Some scholars in the Midwestern grasslands of the United States have also found a positive trend of climate change effects on the annual NPP of grasslands [45]. In the southern United States, [PERSON] also found that temperature changes could enhance or diminish the effects of drought on the NPP in different types of ecosystems, with the interaction of precipitation and temperature changes enhancing the effects of drought on forest productivity and leading to increased productivity declines, but at the same time diminishing the effects of drought on productivity in agricultural and wetland ecosystems. The reduction in the magnitude of drought-induced changes in grassland productivity is supported by the significant increase in grassland NPP as drought severity decreased in grassland ecosystems between 1895 and 2007 [30]. Under the current climate change model, the negative effect of drought on grassland productivity in Inner Mongolia has been reduced in the past 50 years. Figure 10: The net impacts on grassland productivity caused by droughts over the past 50 years. Figure 9: The impacts on grassland productivity caused by precipitation and temperature change over the past 50 years. As shown in Figures 8 and 9, although temperature changes had significant effects on the regional NPP (\(p<0.05\)), the annual variation of the regional NPP average was mainly determined by the fluctuations in precipitation. The maximum NPP appeared in the wettest year and the minimum NPP appeared in the driest year. Figure 11 shows that, in the CLM test mode, the NPP average value under the extreme drought year (2005) was 247.21 gC/m\({}^{2}\)/yr, with a decreased value of 41.51 gC/m\({}^{2}\)/yr (the normal year, 2007) and a larger decreased value OF 127.05 gC/m\({}^{2}\)/yr (the wet year, 1964). In the PREC test mode, the NPP average value (2005) was 223.26 gC/m\({}^{2}\)/yr, with a decreased value OF 55.84 gC/m\({}^{2}\)/yr (2007), AND a larger decreased value of 105.52 gC/m\({}^{2}\)/yr (1964). In the TEMP test mode, the NPP average value (2005) was 228.92 gC/m\({}^{2}\)/yr, with decreased values of 0.62 gC/m\({}^{2}\)/yr (2007) and \(-\)0.35 gC/m\({}^{2}\)/yr (1964). We statistically analyzed the average state of the three years, based on a variation analysis of the regional NPP average values in the typical drought year, normal year, and wet year. As shown in Figure 12, based on the regional SPI_12 data, we classified the 50 years into three types, a drought year, normal year, and wet year. In the CLM test mode, the NPP average value (the extreme drought year) was 266.49 gC/m\({}^{2}\)/yr, with a decreased value of 28.38 gC/m\({}^{2}\)/yr (the normal year, 294.87 gC/m\({}^{2}\)/yr), and a larger decreased value of 66.89 gC/m\({}^{2}\)/yr (the wet year, 333.38 gC/m\({}^{2}\)/yr). In the PREC test mode, the NPP average value (drought year) was 250.38 gC/m\({}^{2}\)/yr, with a decreased value of 31.73 gC/m\({}^{2}\)/yr (normal year, 282.11 gC/m\({}^{2}\)/yr), and a decreased value of 68.6 gC/m\({}^{2}\)/yr (wet year, 318.98 gC/m\({}^{2}\)/yr). In the TEMP test mode, the NPP average value (drought year) was 226.17 gC/m\({}^{2}\)/yr, with a decreased values of 0.54 gC/m\({}^{2}\)/yr (normal year, 226.67 gC/m\({}^{2}\)/yr) and 0.50 gC/m\({}^{2}\)/yr (wet year, 226.67 gC/m\({}^{2}\)/yr). Therefore, in Inner Mongolia, the influence of drought on grassland productivity was mainly controlled by the precipitation deficit, but there were significant interferences in the effects of temperature and precipitation on drought. Some researchers have found that precipitation variation was the main impact factor that led to the reduction of temperate grassland productivity in North China through the global change factor sensitivity simulation test [43]. Figure 11: NPP under CLM experiment for the extremely dry, extremely wet, and normal years based on drought intensity data.