Climate change impacts on water cycle in the Tibetan Plateau: A review

Kun YangInstitute of Tibetan Plateau Research

Chinese Academy of Sciences

The fifth Third Pole Environment Workshop

Berlin, Germany, 2014/12/8-91

Outline

Climate changes over the Tibetan Plateau

Surface water balance changes

Possible causes of glacier and lake changes

Conclusions

22

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 (2000-2006), derived from MODIS data

?

(Qin et al., 2009 Clim. Chang.)4

Cooling

Rapid warming

Warming

Spatial pattern of recent warming/cooling (2000-2006), derived from MODIS data

(Yang et al. 2014, GPC)5

Precipitable water vapor increased during 1979-2011

Lu et al. (2014, JC) 6

Precipitable water vapor increased during 1979-2011, and an abrupt increase occurred in 1998

Lu et al. (2014, JC)7

1998

China TP

Lin et al. (2013, JC)

Wind speed decreased since 1970 but slightly recovered since 2002.

8

Solar radiation decreased since the end of 1970s, due to more Deep Cloud Cover (DCC)

Surface observations Satellite 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

1010

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 it11

RainRadForcings

Land surface modeling at each station

Improved LSM for Arid and semi-arid regions:1. Surface flux parameterization for bare soil surfaces2. Aerodynamic model for sparse canopy 3. High-accuracy soil water flow scheme4. 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

Roff SM

(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 (1988-2008， m3m-3 per 10a)

Spring Summer

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

1

- -

s sg a

g a g ag a

g a g as g s a

e eT rh T

T T T TT TB

B T T T Te T - rh e T

Sensible HeatBowen Ratio

Latent Heat

1 4 CaT . 1 8 CgT . 56rh %

16

Outline

Decadal climate changes over the Tibetan

Plateau

Surface water balance changes

Possible causes of glacier and lake changes

Conclusions

1717

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 1976-2010

（ 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