Regional hydro-climatic changes in the Southern Amazon Basin (Upper Madeira Basin) during the 1982–2017 period

SÖRENSSON, ANNA A.; SEGURA, HANS; CONDOM, THOMAS; RONCHAIL, JOSYANE; GUTIERREZ-CORI, OMAR; WONGCHUIG-CORREA, SLY; ESPINOZA, JHAN CARLO; MOLINA-CARPIO, JORGE; RUSCICA, ROMINA

Journal of Hydrology: Regional Studies

ELSEVIER

Año: 2019 vol. 26

2214-5818

Study region: Upper Madeira Basin (975,500 km2) in Southern Amazonia, which is suffering abiophysical transition, involving deforestation and changes in rainfall regime.Study focus: The evolution of the runoff coefficient (Rc: runoff/rainfall) is examined as an indicatorof the environmental changes (1982?2017).New hydrological insights for the region: At an annual scale, the Rc at Porto Velho station declineswhile neither the basin-averaged rainfall nor the runoff change. During the low-water period Rcand runoff diminish while no changes are observed in rainfall. This cannot be explained byincrease of evapotranspiration since the basin-averaged actual evapotranspiration decreases. Toexplain the decrease of Rc, a regional analysis is undertaken. While the characteristic rainfallrunofftime-lag (CT) at Porto Velho basin is estimated to 60 days, CT is higher (65?75 days) in thesouth and lower (50 days) over the Amazon-Andes transition regions. It is found that 1) thesouthern basin (south of 14 °S) best explains low-level Porto Velho runoff, 2) in the south, rainfalldiminishes and the frequency of dry days increases. Both features explain the diminution of therunoff and the Rc in Porto Velho. Moreover, the increasing dryness in the south compensates forthe rainfall and frequency of wet days (> 10 mm) increase north of 14 °S and explains the lack ofbasin-averaged rainfall trends of the upper Madeira basin.