###### Abstract  
Investigating elevational gradient of climate driving effects on cropland ecosystem net primary productivity (NPP) plays an important role in food security in alpine region. We simulated cropland NPP by coupling a remote sensing model with an ecosystem process model and explored elevational gradient of climate driving effects on it in an alpine region of the southwest China during 1981-2014. The results showed that cropland NPP increased significantly with a rate of 3.85 gC m\({}^{-2}\) year\({}^{-1}\) year\({}^{-1}\) under significant increasing solar radiation and climate warming and drying, among which the increasing solar radiation was the main driving factor of the increasing NPP. The driving effect of climate warming on cropland NPP shifted from negative at low elevations to positive at high elevations, which was caused by the fragile ecosystem characteristics and frequent drought at low elevations and a higher temperature sensitivity of cropland ecosystem at high elevations. Different effects of climate warming on NPP change at different elevations caused different results when we analyzed the climate-driving effects on cropland NPP at different spatial scales. These results reminded us that we should take the elevational gradient of climate driving effects into account when we manage food security in the alpine region. food security; climate change; alpine region with complex topography 202214306  
experienced climate warming and drying during 1982-2014, which caused the increasing of vegetation greenness in the entire region [12]. However, climate warming and drying, especially for the extreme seasonal anomalies of precipitation, have significantly influenced the cropland ecosystem in the alpine region during the past decades [14]. Since the 1990s, ecosystem NPP has decreased in 38% of the total croplands in alpine region [15; 16]. The east and central parts of the Yunnan-Guizhou Plateau are characterized as karst area with fragile surface hydrological system and serious soil erosion [17; 18]. In these areas, increasing in extreme weather events, such as high temperature and seasonal anomalies in precipitation, have caused severe damage to the cropland ecosystem NPP, resulting in a large area of grain-production decline [19; 20]. In 2010, a drought lasting over 6 months reduced ecosystem NPP by 46 Tg C year\({}^{-1}\) across the southwest China [21]. In Yunnan Province and Guizhou Province, the drought resulted in reduction of winter wheat yield by 48% and 31%, respectively [22]. In particular, the probability of climate driving decrease in cropland ecosystem NPP or yield reduction is 2-3 times higher in high-elevation croplands than in low-elevation croplands [12; 23; 24]. At the interdecadal scale, elevation factor is the main controller of NPP pattern and its spatial variation [23]. Elevational gradient of climate change and its driving effects on ecosystem NPP were also reported in other alpine regions and high mountains [25; 26; 27; 28]. However, previous studies related to the cropland ecosystem NPP in the alpine region of the southwest China treated the alpine region as one unity without taking the elevational gradient of climate driving effects into account. Therefore, to improve cropland management, the climate-driving effects must be further investigated in an elevational explicit manner in alpine region of the southwest China. Accordingly, this study simulated temporal and spatial patterns of cropland ecosystem NPP in alpine region of the southwest China during 1981-2014 by coupling a remote sensing model with an ecosystem process model and investigated climate driving effects on cropland ecosystem NPP along increasing elevations. Specifically, we addressed the following questions:  
1. How did climate and cropland ecosystem NPP change from 1982 to 2014 in the alpine region of the southwest China? Did they vary along increasing elevations? 2. Did climate-driving effects on cropland ecosystem NPP vary between different elevations? 3.