Evaluating the impact of the recent temperature increase on the hydrology of the Têt River (Southern France)

The Têt River is a typical Mediterranean river in the South of France where brief and violent flash-floods frequently occur. This paper presents a detailed portrait of the average hydroclimatic patterns in this river basin and investigates their evolution from 1980 to 2000. Average temperatures during this period have been the warmest of the last century, and we intended to find out whether this temperature increase was accompanied by a greater risk of floods, according to the general believe that greater temperatures should lead to an intensification of the water cycle. Average spring temperatures in the basin follow indeed a highly significant trend towards increasing temperatures. Average autumn temperature, however, decreased and counterbalanced partly the spring increase. Mean annual runoff was highly variable and shows no clear trend over the investigated period. But for flood discharge, an evolution towards increasing values can be detected, although only in the downstream part of the basin. Also mean annual precipitation over the entire basin shows no clear evolution, but the contribution from the highest basin parts decreased whereas the contribution from the middle and lower basin parts increased. Our findings suggest that humidity of Mediterranean origin became more important for the hydroclimatic functioning of the Têt basin. If these trends persist in the future, flood frequency of the river may increase.