Topographic effects on solar radiation distribution in mountainous watersheds and their influence on reference evapotranspiration estimates at watershed scale

Abstract

Abstract. Distributed energy and water balance models require time-series surfaces of the climatological variables involved in hydrological processes. Among them, solar radiation constitutes a key variable to the circulation of water in the atmosphere. Most of the hydrological GIS-based models apply simple interpolation techniques to data measured at few weather stations disregarding topographic effects. Here, a topographic solar radiation algorithm has been included for the generation of detailed time-series solar radiation surfaces using limited data and simple methods in a mountainous watershed in southern Spain. The results show the major role of topography in local values and differences between the topographic approximation and the direct interpolation to measured data (IDW) of up to +42% and −1800% in the estimated daily values. Also, the comparison of the predicted values with experimental data proves the usefulness of the algorithm for the estimation of spatiallydistributed radiation values in a complex terrain, with a good fit for daily values (R 2 = 0.93) and the best fits under cloudless skies at hourly time steps. Finally, evapotranspiration fields estimated through the ASCE-Penman-Monteith equation using both corrected and non-corrected radiation values address the hydrologic importance of using topographicallycorrected solar radiation fields as inputs to the equation over uniform values with mean differences in the watershed of 61 mm/year and 142 mm/year of standard deviation. High speed computations in a 1300 km 2 watershed in the south of Spain with up to a one-hour time scale in 30 × 30 m 2 cells can be easily carried out on a desktop PC.

Extreme values of snow-related variables in Mediterranean regions: trends and long-term forecasting in Sierra Nevada (Spain)

“…The average annual precipitation and mean, maximum and minimum average daily temperature for the reference period, 1960-2000, were obtained over the study area in Sierra Nevada, together with selected annual snow related-variables that were simulated during this period using the physical and distributed hydrological model, WiMMed (Herrero et al, 2011; http://www.ugr.es/~herrero/wimmed/), developed and calibrated in this region (Herrero et al, 2009(Herrero et al, , 2011Millares et al, 2009;Aguilar et al, 2010;Aguilar and Polo, 2011;Pimentel et al, 2014). The model includes specific spatial interpolation algorithms for the weather variables to include the abrupt topography of this area , and an energy and water balance snow model.…”

Parameterization of atmospheric longwave emissivity in a mountainous site for all sky conditions

“…CI is the ratio between the theoretical shortwave irradiance at the top of the atmosphere (extraterrestrial radiation) and the surface-measured solar radiation. By means of the CI, calculated with the topographical model described in Aguilar et al (2010), it is possible to find out the degree of opacity of the atmosphere due to the concentration of aerosols and clouds during the daytime.…”

Contribution of Topography and Incident Solar Radiation to Variation of Soil and Plant Litter at an Area with Heterogeneous Terrain

“…Incident solar radiation in a given area is largely determined by terrain topography. Slopes with geographic orientation predominantly facing the equator receive greater amounts of sunlight than those facing opposite directions (Dubayah, 1994;Aguilar et al, 2010). Changes in slope geographic orientation within small distances are common in heterogeneous terrains in tropical regions and create distinct incident solar radiation rates over the soil and litter.…”

“…The amount of incident solar radiation can alter air and soil temperature and moisture (van de Berg and Santos, 2003;Aguilar et al, 2010;Gao et al, 2011). This determines the ionic composition of the soil solution by affecting litter and soil nutrient release rates (García et al, 2006).…”