Compared to the growing number of utility-scale solar farms (USFs) sitting in hilly regions, knowledge of the hydrological behaviors in responding to the installation of USFs in these environments remains limited. We present herein a novel model (the Solar-Farm model) to understand the hydrological behaviors following the construction of a USF in the Loess Hilly Region of China, by combining it with an index of hydrological connectivity (HC). Scenarios were designed to estimate the effects of climate and terrain in controlling the effects of the USF on soil erosion, by altering the mean annual precipitation amount, the frequency of precipitation events, and the relief amplitude. Our results show that land use changes (e.g., vegetation removal) incurred a considerable increase in the accumulative soil erosion (22.45%-66.48%) during the installation period. During the 40-year deployment period, photovoltaic panels (PVs) incurred an average of 0.138 m deeper erosion in the USF compared with the background rate without PVs. A wetter climate induced the highest increase (88.25%) in erosion. However, the relief amplitude and precipitation frequency are also confirmed as important controlling factors for soil erosion (increased by 85.42% and 58%, respectively). The HC was increased during both the construction (0.005-0.12) and operation periods (0.149-0.314). Correlation analysis presented that the landscapes with higher HC were more likely to be exposed to the risks of soil erosion. USFs could increase soil erosion by increasing runoff and local HC, and higher background HC in turn could further aggravate the effects of USFs on soil erosion.

Desert pavements are critical for maintaining ecological stability and promoting near-surface hydrological cycle in arid regions. However, few studies have reported the desert pavements on ecological on fluvial fans. Although desert pavement surfaces appear to be barren and flat, we found that the surfaces were featured by mosaic pattern of desert pavement (DP) and bare ground (BG). In this study, we investigated the effects of mosaic DP on water infiltration and vegetation distribution at six sites (i.e. one on the hillside and five in the sectors of fluvial fans) along a southwest belt transect on the fluvial fans in the Northern Linze County, in the middle of Hexi Corridor. The results showed that significant differences of Mosaic DP between hillside and sectors of fans were found in pavement thickness, thickness of vesicular horizon (Av thickness), particle composition and bulk density, rather than soil moisture content (SMC), gravel coverage and surface gravel size. The mosaic DP can inhibit water infiltration by pavement layer, where the sorptivity (S), initial infiltration rate (iint) and steady- state infiltration rate (isat) and infiltration time (T) averaged 1.30 cm/min-0.5, 5.03 cm/min, 0.23 cm/min, and 12.76 min respectively. If pavement layer was scalped, the S, iint and isat increased by 0.75 cm/min-0.5, 2.90 cm/min and 0.13 cm/min, respectively, and the T was shortened by 5.34 min. Water infiltration was mainly controlled by the pavement layer thickness (+), Av thickness (-), surface gravel coverage (-), and fine earth (+) and fine gravel (-) of pavement layer. Mosaic DP grew less shrubs than mosaic BG where distributed plenty of herbs. It can be concluded that desert pavements can keep vegetation stability by self-regulating rainfall. This study would deepen our understanding of the eco-hydrological cycle of pavement landscape in arid regions.

A knowledge of the exchanges of energy and water over the terrestrial surface is the first step to understand the ecohydrological mechanisms, particularly in water-limited ecosystems in the dryland environments. However, patterns of energy exchange and evapotranspiration (ET) are not well understood in the oasis-desert ecotone, which plays an important role in protecting oasis against the threat of desertification in northwestern China’s arid regions. Here the continuous measurements of surface energy fluxes were made using eddy covariance in conjunction with auxiliary measurements for two years (2014-2015) at a shrubland within an oasis-desert ecotone in the arid regions, northwestern China. Statistical analysis on 30-min time scale indicates that about 50% of daytime net radiation (Rn) over the shrubland is dissipated as H on average, which peaks in spring; one third Rn is consumed by soil heat flux (G). Only 9% of Rn was consumed for latent heat flux (λE), which peaks in summer (21% in 2014 and 16% in 2015), corresponding to the season with highest rainfall among all seasons. Daily mean ET is about 1 mm·d−1 during growing season of the shrub species. The rapid and transient increase in ET occurs following a rainfall event. A switch in surface soil moisture from 0.04 to 0.11 m3·m−3 causes an increase in Rn by about 11% and λE by 151% at the shrubland, respectively. Accumulated annual ET were 195 and 181 mm in 2014 and 2015, respectively, exceeding the corresponding P by about 87 and 77 mm, indicating that groundwater may be another important source of water for ET over the shrubland aside from P. These results provide valuable insight into the mechanisms of sustaining energy and water balance at the ecotone, and then produce some management guidelines for allocating water resources and protecting vegetation.

Desert pavements are the common features widespread in arid region, which are important for regulating the ecological and hydrologic processes. However, few studies focused on the role of water movement in maintaining ecologic function in desert pavement landscapes. This study determined the role of desert pavements in water infiltration on fluvial fans, which were reflected by characteristics of desert pavements and infiltration parameters in the middle reaches of Hexi Corridor. Six sites (i.e. one site in hill slope and other five sites in the piedmont) were selected for surveying soil properties within a 50-cm depth soil profile and measuring sorptivity (S), initial water infiltration (ii), steady-state infiltration rate (is) and infiltration time (T) in crust and scalped crust conditions under 5-cm pressure head. The results indicated that desert pavement surfaces were covered by a thin layer of protective crusts, which were primarily composed of fine earth (56.94%) and fine-medium gravel (40.46%). Although characterized by a big range of gravel coverage (19.48%- 97.63%), the crusts had small gravels (mean size: 0.58 cm) and extremely low soil moisture content (SMC; less than 1.30%), which two parameters did not significantly differ from each site in fluvial fans. The crusts were effective in restricting water infiltration capacity. When the crusts were scalped, the S, ii and is would improve 1.6, 1.7 and 1.6-fold, respectively. These three parameters significantly increased with gravel coverage and medium gravels, but significantly decreased with crust thickness and fine gravels. Desert pavements were closely with water regulation in arid systems, reflecting the vegetation distribution. This study highlights that desert pavements have a strong impact on water infiltration to function as regulating water resource and supplying water for vegetation growth.