Precipitation plays an important and crucial role in processes in the water-wind erosion crisscross region of the Loess Plateau than in other parts of the region. We analyzed precipitation data and standardized precipitation index (SPI) at 14 representative synoptic stations from 1958 to 2015 used trend-free prewhitening, linear trend estimation, Spearman’s rho test, the Mann-Kendall trend test, the Mann-Kendall abrupt change test and rescaled range analysis. The following conclusions were drawn. First, the analysis of monthly precipitation at all stations suggested that precipitation during the rainy season (July, August, September), especially rain in July and August, exhibited a general decreasing trend, while both increasing and decreasing trends were observed in other months. Moreover, the annual precipitation of all stations continued to exhibit decreasing trends except Wuzhai. Erosive rainfall frequency in the rainy season and the annual scale was weakly reduced but erosive force of single rainfall has been enhanced. Second, the SPI exhibited different increasing degrees in winter, while decreasing trends were observed in other seasons. Additionally, the annual-scale SPI at most stations exhibited a stable and sustained downward trend. Therefore, this region is currently associated with a drought trend, and the drought degree will likely continue to increase.

Exposed, steep earthy road slopes (ESERs) in the semiarid loess region of China are prone to soil erosion and are difficult to revegetate. Topsoil desiccation (TSD) leads to land degradation, which limits the revegetation success. In this study, TSD was assessed on southfacing ESERs (with slopes of 45-55°, 55-65°, 65-75°, and >75°), and a revegetation method using the deep planting of container seedlings of 3 species (both native and introduced species) was designed to overcome the problems associated with TSD. Plant growth was evaluated by measuring plant height and diameter of the stem base after 4 growing seasons. The following results were obtained: (a) TSD occurs on south-facing ESERs and persists after the rainy season. The thickness of the TSD layer remained at approximately 15 cm (<20 cm for all studied slope grades) on the slopes with a formation time of approximately 3 years as of the beginning of this study, and the thickness increased to 35-40 cm on the control slope after 4 years of the study. (b) Using the deep planting of container seedlings method, plant roots can completely penetrate the TSD layer. The selected native species (Caragana korshinskii Kom. and Tamarix chinensis Lour.)and introduced species (Caryopteris clandonensis 'Worcester Gold') all survived; among them, T. chinensis Lour. exhibited the best growth and the best adaptation to changes in slope grade. The applied method can also effectively inhibit further increases in TSD and can be used in semiarid loess regions and similar areas.

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The loess hilly-gully region is a focus region of the “Grain for Green” program in China. Drought is the main problem in the study region. Precipitation and temperature are two indicators that directly characterize climatic drought. A thorough analysis of the precipitation, temperature and drought characteristics of the loess hilly-gully region can clarify the current water and heat conditions in the region to improve regional water resource management and provide a reliable reference for effectively improving water use efficiency. In this study, we fully analyzed the precipitation and temperature characteristics at 11 representative synoptic stations in the loess hilly-gully region over the period from 1957 to 2014 using a combination of trend-free pre-whitening, linear trend estimation, Spearman’s rho test, the Mann–Kendall (M-K) trend and abrupt change tests and wavelet analysis. The standardized precipitation evapotranspiration index was calculated and analyzed on different time scales. The following conclusions were drawn: (1) There were significant spatial differences and inter-annual variations in precipitation at the 11 synoptic stations in the study area between 1957 and 2014; the precipitation consistently decreased with fluctuations, and the extent of the decrease varied from a maximum of 17.74 mm/decade to a minimum of 2.92 mm/decade. Except for the downward trends of the autumn and winter mean temperatures at Hequ, the seasonal and annual mean temperatures at the stations showed upward trends, including highly significant upward trends. (2) Alternating drought and wetness occurred in the study area; the wet period mainly appeared in the 1960s, and the main dry period lasted from the late 20th century to 2012. There were fewer dry and wet years than normal years; however, the study area still showed a drying trend, and the severity of the drought was increasing. (3) The annual precipitation and annual mean temperature showed marked cyclical fluctuations at each synoptic station, and the first primary cycle was approximately 28 years. The seasonal precipitation and seasonal temperature showed different cycle lengths; the seasonal cycles of precipitation for spring, summer, autumn and winter were 10, 28, 10 and 26 years long, respectively, and the cycles of the temperature fluctuations for all four seasons were approximately 28 years long.