River Runoff Sensitivity in Eastern Siberia to Global Climate Warming

During several last decades significant climate warming is observed in permafrost regions of Eastern Siberia. These changes include rise of air temperature as well as precipitation. Changes in regional climate are accompanied with river runoff changes. The analysis of the data shows that in the past 25 years, the largest contribution to the annual river runoff increase in the lower reaches of the Lena (Kyusyur) is made (in descending order) by the Lena river watershed (above Tabaga), the Aldan river (Okhotsky Perevoz), and the Vilyui river (Khatyryk-Khomo). The similar relation is also retained in the case of flood, with the seasonal river runoff of the Vilyui river being slightly decreased. Completely different relations are noted in winter, when a substantial river runoff increase is recorded in the lower reaches of the Lena river. In this case the major contribution to the winter river runoff increase in the Lena outlet is made by the winter river runoff increase on the Vilyui river. Unlike the above cases, the summer-fall river runoff in the lower reaches of the Lena river tends to decrease, which is similar to the trend exhibited by the Vilyui river. At the same time, the river runoff of the Lena (Tabaga) and Aldan (Verkhoyansky Perevoz) rivers increase. According to the results of hydrological modeling the expected anthropogenic climate warming in XXI century can bring more significant river runoff increase in the Lena river basin as compared with the recent one. Hydrological responses to climate warming have been evaluated for the plain part of the Lena river basin basing on a macroscale hydrological model featuring simplified description of processes developed in Institute of Geography of the Russian Academy of Sciences. Two atmosphere-ocean global circulation models included in the IPCC (ECHAM4/OPY3 and GFDL-R30) were used as scenarios of future global climate. According to the results of hydrological modeling the expected anthropogenic climate warming in 21st century can bring much more significant river runoff changes in plain part of Lena river basin compared with the 20th. The both scenarios suggest quite a significant change in the character of the annual stream-flow distribution in middle of XXI. The scenarios give, in essence, the similar pattern of changes in the wave of spring-summer high water. The onset of the flood can be shifted one month backward, as compared with the current situation. The main contribution to the river runoff change in the mid-21st century can be made by the increase in atmospheric precipitation and air temperature, while the scenario changes in the active layer depth are not to make a perceptible impact. This study was supported by NASA grant NNG06GH41G and the Russian Fund on Basic Research grant 07- 05-12085-ofi.