Abstract

Good estimations of the surface temperature lapse rate (STLR) and the 0 °C isotherm are fundamental for hydrological modeling of high-relief environments and mountainous basins. Even though STLR changes in space and time, it is typically assumed to be constant, which can lead to errors in hydrological modeling and flash-floods risk assessment. This work characterizes empirically the daily and seasonal temporal dynamics of the in-situ STLR and 0 °C isotherm in the central Chilean Andes. We used temperature data collected during two years every 10 min by a dense network of sensors deployed in a small catchment with elevations ranging between 700 and 3,200 m. Resulting values are compared against those obtained using off-site publicly available data sets. Significant intra- and inter-day variations of the in-situ STLR were found, with values being smaller and more constant for wet-weather conditions, regardless of the season. Moreover, the average in-situ STLR during rainfall events with the 0 °C isotherm located above 3000 m (i.e. warm events) is -4.6 °C/km, 1.4 °C/km larger than for non-warm events (-6.0 °C/km), and significantly higher than the standard atmospheric lapse rate of -6.5 °C/km typically used in the analysis and modelling of flash floods caused by the warm evens in the area. On the other hand, STLR and 0 °C isotherm estimations using off-site gauges are extremely sensitive to counting with gauges located at a high elevation. Also, regional atmospheric sounding data allow a good estimation of the 0 °C isotherm during wet-weather conditions although the free-air temperature lapse rate is not representative of the STLR.