Climate change impacts on water cycle in the Tibetan Plateau: A review Kun Yang Institute of Tibetan Plateau Research Chinese Academy of Sciences The fifth Third Pole Environment Workshop Berlin, Germany, 2014/12/8-9 1

Outline  Climate changes over the Tibetan Plateau  Surface water balance changes  Possible causes of glacier and lake changes  Conclusions 2 2

Moistening Dimming Warming Stilling (Yang et al. 2014, GPC) The Tibetan Plateau has been experiencing a rapid climate change since middle of 1980s: warming, moistening, wind stilling and solar dimming 3

The warming rate changes with elevation ( ), derived from MODIS data ? (Qin et al., 2009 Clim. Chang.) 4

Cooling Rapid warming Warming Spatial pattern of recent warming/cooling ( ), derived from MODIS data (Yang et al. 2014, GPC) 5

Precipitable water vapor increased during Lu et al. (2014, JC) 6

Precipitable water vapor increased during , and an abrupt increase occurred in 1998 Lu et al. (2014, JC)

China TP Lin et al. (2013, JC) Wind speed decreased since 1970 but slightly recovered since

Solar radiation decreased since the end of 1970s, due to more Deep Cloud Cover (DCC) Surface observationsSatellite observations (Yang et al. 2012, GRL) 9

Outline  Decadal climate changes over the Tibetan Plateau  Surface water balance changes  Possible causes of glacier and lake changes  Conclusions 10

How surface water balance responded to climate change? The number of CMA stations is not sufficient to support water balance analysis at basin-scale by DHM; instead, we use a land surface model to simulate it 11

Rain Rad Forcings Land surface modeling at each station Improved LSM for Arid and semi-arid regions: 1. Surface flux parameterization for bare soil surfaces 2. Aerodynamic model for sparse canopy 3. High-accuracy soil water flow scheme 4. Soil freezing and thawing (Yang et al. 2009, HESS) 12

Hydrological cycle response: more runoff in central TP and less runoff in south/east TP P E RoffSM (Yang et al., 2011 Clim Change) 13

Evaporation derived by data fusion of GLDAS simulations and GRACE gravity data shows increasing trends in both east and west. Li et al. (2014, JGR) Qiangtang Qaidam Yangtze Yellow 14

The positive trend in soil moisture also supports northwestern TP got wet ( ， m 3 m -3 per 10a) SpringSummer Autumn Northwestern TP (Velde et al. 2014, HESS) 15

Yang et al. (2014, GPC) Sensible heat decreased The evaporation increase is consistent with sensible heat decrease found in recent studies. This may be explained by the response of Bowen ratio to warming 16

Outline  Decadal climate changes over the Tibetan Plateau  Surface water balance changes  Possible causes of glacier and lake changes  Conclusions 17

Glacier change and its possible causes Cooling Rapid warming Stable or extend Rapid shrink Moderate shrink Warming Yang et al. (2014, GPC) 18 (Yao et al. 2012, NCC) Surface warming/cooling spatial pattern also corresponds well to the spatial pattern of glacier changes (Yao et al. 2012, NCC)

Observed lake changes: expanded in central and northwestern TP and shrank in south TP （ Lei et al, 2014, Climatic Change ） 19 Rapid shrink Rapid warming

Relationship between lake expansion and glacier/lake area ratio in interior TP during （ Lei et al, 2014, Climatic Change ） 20 Non-glacier-fed lakes expanded, too. Glacier melt does not dominate lake changes but seems accelerating the expansion.

Lake area change is highly correlated with the accumulation of precipitation anomaly （ Lei et al, 2014, Climatic Change ） 21

Water vapor changes correlates with large-scale indices NHSM circulation intensity: V850-V200 HTC: hemispheric thermal contrast AMO: Atlantic multi-decadal oscillation mega-ENSO” index: SST difference between the western Pacific K-shape area and eastern Pacific triangle as （ Lei et al, 2014, Climatic Change ） 22

Conclusions Dry (Central and Western TP) got less dry, and wet (Southern and Eastern TP) got less wet. Evaporation increased overall, which is a response to warming. Glacier change may be related to the spatial change of both precipitation and air temperature. Lake changes are mainly due to precipitation increasing/decreasing, and glacier melt may have accelerated lake expansion. An integrated model is needed to understand the processes of these changes. 23

Simple water balance calculation without glacier and frozen soil explains lake level changes except Nam Co Lei et al. (2013) 24