## Results
### Effects of Clouds
In fact, the recent weakened rainfall and dried monsoon during the summer monsoon season were verified by many previous studies, given the reduction of clouds [49; 51]. Consequently, we investigate the radiative force of cloud vertical variations to determine their possible contribution to the recent rapid brightening (Figure 4). We use the vertical heating rates in all-sky conditions to indicate the change in the vertically radiative effects of clouds. These effects are the results of cloud fraction, cloud vertical distribution, and cloud microphysical properties [26]. The SW heat rating decreased by around 0.3-0.4 K d\({}^{-1}\) at an altitude of 5-15 km from 2006 to 2015, whereas a few increases in the SW heat rating occurred at low-level and near-surface areas (below 3 km). The total cloud reflection and absorption (mainly located at 5-15 km) weakened consistently with the reduction in clouds, thereby enhancing atmospheric transmission, causing further SW radiation to reach the near-surface area, and heating the low-level atmosphere and surface [24]. Because of the extremely minimal cloud detected by CloudSat at above 15 km, no significant change in heat rating occurred above 15 km, as demonstrated in the cloud vertical frequency distribution shown in Figure 2a. However, the change in LW vertical heating rate was indistinct compared with that of SW. Correspondingly, the LW radiative heating increased by less than 0.2 K d\({}^{-1}\) above 10 km, whereas that of heating decreased by 0.1-0.2 K d\({}^{-1}\) within the cloud, especially below 3 km, from 2006 to 2015. The total cloud LW absorption emitted from the surface decreased with the reduction in clouds, thereby leading to a weakened LW heating rate within the cloud layer (mainly below 10 km) and more LW emissions on the top cloud layer above 10 km [18]. In general, the net vertical heating rate weakened consistently, thereby indicating that the changes in the physical characteristics of clouds result in the weakened vertical radiative effect of clouds. When a cloud layer occurs, the incident solar radiation at the surface is generally reduced due to the absorption and reflection of cloud layers to solar radiation [24]. In Figure 5a, the SW CRE at the surface and TOA is weakened by approximately 42.1 and 38.5 W m\({}^{-2}\) with high significance levels \(p\) of 0.05 and 0.04, respectively. This phenomenon indicates that the total absorption and reflection of cloud layers to solar radiation is weakened due to the cloud property variations, which thus leads to  
Figure 4: Temporal variations in spatial average vertical (**a**) SW, (**b**) LW, and (**c**) net heat rating in all-sky conditions from CloudSat during the monsoon season in South Asia from 2006 to 2015.  
consequentially enhancing the incident solar radiation at the surface. Although the CRE, derived from CloudSat, largely ignores the contribution of high thin clouds, this contribution is considerably smaller than that of low clouds [18; 24]. Figure 5b presents the spatial distribution of the weakened SW CRE at the surface, which is the result of cloud property variations (Figure 3). The weakened SW CRE reaches its maximum and minimum in the central and northwest parts of South Asia, respectively. This spatial pattern of the weakened SW CRE is possibly attributed to complicated and diverse factors, including cloud spatial distribution (minimal cloud in the northwest part of South Asia), aerosol distribution (maximum in the central and northern part of South Asia), and terrain [38].