Abstract
Mountain areas are considered world water towers. They constitute about 27% of the emerging area and are the main source of water resources for downstream areas, providing about one to two thirds of the total global freshwater. In the current global warming situation these areas are especially vulnerable. The increasing temperature and the changes in precipitation patterns are modifying snow seasonality, among others, actual snowfall volumes and the timing of melting onset. These snow variations have an impact on annual streamflow dynamics; however, how is the link between snow and streamflow? Despite years of research, when responding to this question no clear answer is found in the scientific literature. For instance, there is not a demonstrated connection between the decline in snowfall and the decline in streamflow or between the variation in snow cover fraction and the changes in timing in melting onset.
This work aims at evaluating the nexus between snow and streamflow in mountain areas worldwide in the last two decades. For that, snow and streamflow indicators are defined over 548 catchments in different mountain areas worldwide in which at least 10% of their area is covered by snow yearly. In situ streamflow observations and MODIS products are used respectively. Annual mean streamflow volume, maximum streamflow, time of the spring peak are some of the indicators defined for the streamflow. In the case of the snow, average snow cover area, duration of the snow season and first and last days with snow within the hydrological year are selected as indicators. Over these indicators, two analyses were carried out. First, actual values were assessed by assessing correlation between variables. Second, significant statistical trends analysis were derived over snow and streamflow parameters to understand the connection and impact between them.
The preliminary results show that on a yearly basis, only 16% of the catchments show a significant linear correlation between annual mean streamflow and average snow cover area. However, only around 5% of the catchments are affected with significant trend changes in both snow parameters and streamflow. In the location where this happened, snowmelt occurs early with an average value of 28 days and snow cover fraction reduction about 15% and a decrease in annual mean streamflow of 67 m3/s over the whole period. When analyzing the spatial distribution the more affected areas are located in the Andes Cordillera in South America.