Hydroclimate in Eurasia from the Arctic to the Tropics

Abstract

Hydrometeorology in Eurasia connects the Arctic with lower latitudes through exchanges in moisture and teleconnections influencing climate variability. This thesis investigates the role of dams on the Kolyma basin, of precipitation and temperature change on a pristine permafrost lined basin of the Yana, and of changing snow cover over Eurasia on the Indian Monsoon. These three pieces of work illustrate different aspects of a changing climate that impact Eurasian hydrometeorological variations. The Kolyma is one of the large rivers which flows into the Arctic Ocean where there has been a large winter increase and summer decrease in flow over the 1986-2000 period. Winter months are characterized by low flow while summer months by high flow. Reservoir regulation was identified as the main cause of changes in the discharge pattern, since water is released in winter for power generation and stored in summer for flood control. The overall discharge to the Arctic Ocean has decreased for Kolyma basin, despite the increase during winter. This study documents how human activities (particularly reservoirs) impact seasonal and regional hydrological variations. The Yana Basin is a small pristine basin that has experienced minimal human impact and is ideal for investigating the role of climate variability on discharge. The precipitation discharge and temperature discharge analysis for Ubileinaya suggests that increased precipitation and higher temperatures resulted in higher discharge, but other parameters also come into play since greater precipitation does not always yield higher discharge. Overall our analysis for this station has increased our understanding of natural basins and how the climate variables like precipitation and temperature play a role. Recent increases in May-June Indian monsoon rain fall were investigated in the context of Eurasian snow cover variations since the onset of the monsoon has long been linked to Himalayan snow cover. Himalayan snow cover and depth have decreased and this study argues that this is the driver of increased rainfall during May-June, the pre-monsoon and early monsoon period. In addition, there has been an increase in snow water equivalent in Northern part of Eurasia and decrease in Southern part, suggesting that the anomalies are large-scale. Storm track analysis reveals an increase in the number of storms in northern and a decrease in southern Eurasia. The large-scale Eurasian snow increases have been shown by other studies to be linked to Arctic sea ice decline. The direct linkage between fall Arctic sea ice decline and an increase in May-June Indian monsoon rainfall is proposed in this work but the exact climate mechanism is tenuous at this point. This study is focused on understanding changing Arctic rivers and the connection of the Arctic with the Indian monsoon. Our study has shed some light into the connection between the Arctic and the tropics. This study could benefit from modeling study where we could have case study with and without sea ice to understand better how that could impact the monsoon and the hydrological cycle in the present and the future. Better understanding of the mechanism would help us take steps towards better adaptation policies.