Since 1999, the Loess Plateau, China, has undergone one of the world's largest revegetation programs (Grain for Green Project, GfGP). Revegetation has profound impacts on hydrological cycle and water balance, especially in arid and semi‐arid areas. As an essential component of water balance, the long‐term change in water storage (ΔS) is generally treated as zero. However, it remains unclear how to define the time scale of “long‐term,” especially over regions undergoing dramatic vegetation restoration. In this study, we quantify ΔS over the Loess Plateau from 1982 to 2009 from a water balance perspective, with a particular focus on the impact of vegetation on ΔS at different time scales. Results show that a 44.78% increase in vegetation coverage could lead to a 37.72% decrease in ΔS. Moreover, the better the vegetation growth, the lower the ratio of ΔS to precipitation (ΔS/P) in the Loess Plateau. ΔS/P achieved a local minimum at the 4‐ to 5‐year scale and reached a plateau after 10 years. We further use the Budyko framework to verify the above conclusions. We find that errors of simulated streamflow over 11/16 of catchments become stable after 4–5 years, and all 16 catchments become stable after 10 years. Ignoring ΔS at a 10‐year scale has the least influence on water budget closure. These findings highlight the importance of considering time scales when ignoring ΔS in the water balance analysis, especially when the length of measurement is limited.

Afforestation is a major anthropogenic forcing to the global and regional climate. However, the biophysical impacts of large‐scale afforestation on local temperature in temperate regions remain unclear, due to the closely matched but compensating radiative and non‐radiative effects. The Grain for Green Program (GFGP) is a large‐scale afforestation program implemented over the Loess Plateau (LP) in China. The GFGP thus provides an ideal platform to explore the temperature effect of afforestation. This study investigated such a temperature effect through long‐term, high‐resolution simulations incorporating satellite observations in a coupled land‐atmosphere model. With an optimal combination of physical schemes proposed by this study, we greatly improved the accuracy of regional climate modeling. The results reveal that the afforestation caused a significant decline (−0.50% yr⁻¹) in albedo. An increment in net shortwave radiation mainly led to an increment in net radiation (7.95 W m⁻²). The afforestation also led to an increment in sensible heat flux (3.78 W m⁻²). Consequently, the afforestation caused a warming effect (0.36°C) in 2‐meter air temperature at the inter‐annual scale. At the intra‐annual scale, there was a cooling effect in July and August, while other months demonstrated a warming effect. The radiative effect dominated local temperature change induced by the afforestation over the LP. Therefore, the large‐scale afforestation contributed to the local warming trend. Our findings highlight the temperature effect of afforestation, and imply that more attention should be paid to future revegetation to carefully assess its potential influence on regional climate.