Characteristics of solar radiation distribution and albedo in Yuanjiang dry-hot valley, Southwest China

Based on the continuous observation data of solar radiation (SR) through two years(from May 2013 to April 2015)in a dry-hot valley in southwest China's Yuanjiang, daily, seasonal and annual variations of SR components above the canopy of open shrubland were addressed. Meantime, values of SR components, e.g., total global radiation (Q), reflective radiation (Qα), effective radiation (I) and net radiation (Rn) related to global radiation and variations of albedo (α) as well as its driving factor were investigated. The results showed that yearly average of Q, Qα, I and Rn were 6 210.2, 807.9, 1 822.9, 3 578.7 MJ/(m2·yr), respectively, and the ratios of Q, Qα, I, Rn in rainy season to yearly average value were 52.9%, 56.3%, 39.1%, 59.2% separately. Except for the seasonal variations of I appearing higher value in rainy season than that in dry season, Q, Qα and Rn in rainy season were higher than those in dry season. Albedo (α) in dry season was lower than that in rainy season because of the increasing leaf area index (LAI) and canopy closure extent in rainy season, and this is also the result of long-term evolution ecological strategy of local ecosystem to reduce evaportranspiration (ET) and increase net primary production. The annual distribution ratios of Qα, I and Rn were 13.0%, 29.8% and 56.9% separately. The seasonal variations in the distribution ratios of Qα and Rn were both higher in rainy season than those in dry season; however, the distribution ratios of I showed an opposite seasonal variations pattern. The increasing distribution ratios of I in dry season decreased land surface and canopy temperatures, reduced ET of ecosystem, weakened drought stress of ecosystem in dry season and avoided vegetation death due to the damage of hydraulic architecture inducing carbohydrate starvation, which is beneficial to vegetation survival in dry season and maintain the ecosystem balance in Yuanjiang dry-hot valley. As Q and Rn of Yuanjiang hot-dry valley vegetation were higher and considering the precipitation in this region was just about 700 mm, thus human activities and climate change are more likely to affect this ecosystem balance.