Laboratory for
Climatology and Remote Sensing

Abstract:

Global evidence indicates that orography can exert a strong influence on rainfall, thereby giving rise to natural hazards such as flooding in mountain areas. Alongside orographic influences, urban areas can also act to intensify storms, but their impact on heavy rainfall in high elevations has not yet been investigated in detail. Here, we quantify the contribution of a high-altitude city to both rainfall intensification and its daytime and nighttime patterns, focusing on the city of Cuenca in the Ecuadorian Andes. Modeling several observed storms with and without the city suggests that the urban area can enhance downstream precipitation by over 20% over a pre-existing hotspot of orographically induced precipitation. This urban-induced rainfall intensification seems to exceed that observed for cities of comparable size outside mountainous regions. This may be explained by Cuenca’s valley setting and its high humidity compared to its surroundings, suggesting that high-altitude cities with similar morphologies could amplify combined orographic-dynamic and urban-thermodynamic effects.

Abstract:

Reference evapotranspiration (ETo) is often calculated using the Penman-Monteith (FAO 56 PM; Allen et al 1998) method, which requires data on temperature, relative humidity, wind speed, and solar radiation. But in high-mountain environments, such as the Andean páramo, meteorological monitoring is limited and high-quality data are scarce. Therefore, the FAO 56 PM equation can be applied only through the use of an alternative method suggested by the same authors that substitutes estimates for missing data. This study evaluated whether the FAO 56 PM method for estimating missing data can be effectively used for páramo landscapes in the high Andes of southern Ecuador. Our investigation was based on data from 2 automatic weather stations at elevations of 3780 m and 3979 m. We found that using estimated wind speed data has no major effect on calculated ETo but that if solar radiation data are estimated, ETo calculations may be erroneous by as much as 24%; if relative humidity data are estimated, the error may be as high as 14%; and if all data except temperature are estimated, errors higher than 30% may result. Our study demonstrates the importance of using high-quality meteorological data for calculating ETo in the wet páramo landscapes of southern Ecuador.