Global Change of Hydrology and Flood Risk in a Changing Environment

Qiuhong Tang

Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences

Global Flood Partnership Conference 2019

11-13 June 2019 · Guangzhou, China

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Global Change Hydrology: An Emerging Discipline

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Water Related Hazards

Emerging challenges of water related hazard require understanding the global water system and the natural and human-induced factors that influencing the water system.

2012/Beijing

Over 90% natural hazards are water related, including drought and

flood (United Nations Environment Programme).

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Global Water System

Humanity has become an important driving force of changes to the Earth’s hydrosphere and hydro-hazards.

Climate extremes

Hydrological

extremes

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Global Change Hydrology

Global Change Hydrology, an emerging discipline representing an evolution of hydrological sciences towards the linkage with global environmental change for understanding and quantifying the human fingerprint in the global water system.

Global Change

Hydrological Sciences

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Scales in Hydrology

Global Change Hydrology can be across scales.

Anne Van Loon, 2015

Global

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1. How to depict the broad array of human-induced factors in a human-water model?

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Bucket Model

It considers the impact of human-induced climate change.-15

-5

5

15

25

35

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1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86 91 96 101 106 111 116 121

Tang and Oki, 2016. Terrestrial Water Cycle and Climate Change, AGU Geophysical Monograph

Hydrological model

9Tang 2006.

Land Surface Model (LSM)

Vegetation

Soil

Snow

Permafrost

Runoff

It considers the impact of changes in underlying surface (including vegetation, snow, permafrost)

Land cover and land use change

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LSM with water management

1) Water demands

Wilting Point

Targeted Soil Moisture Level

Requirement

A B C D

A

D

CBO

O

➀

➀

➀

➀ Vegetation condition-hydrology

➀ Climate (Energy part)-hydrology

➀ Human activity-hydrology

Contributions:

Biosphere (SVAT scheme)

New features:

Non-Irrigated Irrigated

1.0 IF

IF: Irrigation fractionIrrigation

Groundwater withdrawals

Tang, JHM 2007, J Climate 2008; Leng et al. 2014

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LSM with water management

Liu et al. 2016

Reservoir model

2) Water supply

It considers the impacts of water management.

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The Distributed Biosphere-Hydrological (DBH) model

Tang et al. JHM 2007.

SVAT scheme

Mass/Energy

Photosynthesis

CO2

Hydrologic scheme

Human activity

Nontraditional

data sourcesClimate model

Snow meltChemical tracers

The model is a coupled

human-water model that

can represent most major

human-induced factors

that influencing the

terrestrial water cycle.

Human Water Use

(Irrigation)

SiB2

Simple Biosphere Model

Climate Change

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2. How to separate human and climate impacts on the hydrological cycle?

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Yellow River run dry in the 1990s

Source: YRC; Yang et al. 2004

Drying days (zero low)

Huang et al. 2009

Red -crowned Crane

North

China

Plain

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What factors contribute to the drying?

Change in Temperature

Change in Precipitation

Source: Tang et al. 2008

Candidate Factors• Climatic Changes• Water withdrawals• Vegetation changes

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Model settings

Photo credit: Sina, Hudong wiki, Yellowriver.gov.cn

DBH enables direct comparisons with the managed flow, rather than the ‘naturalized’ flow.

794,712 km2

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Effects of irrigation

TNHLZ

QTX

TDG

LM

SMXHYK

LJ

Evaporation increases

2.1 6.9 10.5 22 0AVG ID IF3 MAX MIN

Surface temperature decreases

-0.1 -0.32 -0.4 0 -1.6AVG ID IF3 MAX MIN

Averaged (AVG) In Irrigation Districts (ID) Irrigated Fraction>0.3(IF3) MAXimum MINimum

TNH LZ QTX TDG LM SMX HYK0

500

1000

1500

2000

2500

Dis

ch

arg

e a

lon

g r

ive

r (m

3/s

)

Observed

Case 1

Case 2

Case 3

Case 2_ No irrigation

Case 3_ With irrigation

60%

40%

Observed

With Irrigation

Without Irrigation

Source: Tang et al. 2007 From upstream to downstream

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Major drivers contributing to the drying

Upper Reaches Middle Reaches Lower Reaches

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3. How to assess water-related risks and build resilience?

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Climate change impact assessment

Climate Change Scenarios

(RCPs)

Assessment Model (DBH)

Socio-economic Change Scenarios

(SSPs)

Impacts on water, agriculture, …

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Climate Change Impacts

Schewe et al. PNAS 2014

Elliott et al. PNAS 2014

Relative change in annual discharge at 2 oC compared with present day, under RCP8.5.

Median potential end-of-century renewable water abundance/deficiency in average cubic kilometers per year under RCP 8.5

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Risks at different sectors

Identified areas with high risk.Liu et al.; Yin et al.

Hydropower

Crop yield

HeatwaveEcosystem shift

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Risk atlas under climate change

Tang & Ge (Eds) 2018

Map license: JS-(2016)01-143

With the risk atlas, scientific knowledge can be translated to policy and management practices.

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Flood Risk in a Changing Environment

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Projected change in flood frequency. Multi-model median return period

(years) in 21C for discharge corresponding to the 20C 100-year flood.

Increasing flood frequency under climate change

Hirabayashi et al. 2013

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A large portion of people lives in flood-prone area

Europe

Managed

surface

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Modeling with flood control measures

The Baiyangdian Lake Basin The Xiong’an New Area

Established in April 2017, the Xiong’an

area is located about 100 km southwest

of Beijing. Its main function is to serve

as a development hub for the Beijing-

Tianjin-Hebei economic triangle.

Dams at upper

reaches

LakeDikes

City

The Lake

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Experimental design

• Exp 1: Flood risk of a historical 50-year flood (the August

1963 flood)

• Exp 2: Present flood risk, using the same historical 50-

year flood with the flood control works

• Exp 3: A future 50-year flood with the heightened dike

and reservoirs

The historical 50-year design storm was estimated based on the

historical observations.

The future 50-year design storm was estimated using the bias-

corrected climate data from five general circulation models

(GCMs) (HadGEM2-ES, GFDL-ESM2M, IPSLCM5A-LR,

MIROC-ESM-CHEM, and NorESM1-M) under the RCP8.5

scenario from ISI-MIP.

Wang et al. HSJ 2019 accepted

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50-year storms

The 50-year design storm for the historical (1952-2010) and

future (2032-2090) periods.

311 mm

379 mm

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50-year floods

The 50-year design flood into the lake for the historical

(1952-2010) and future (2032-2090) periods.

Without

Reservoirs

With Reservoirs

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Results: inundation area

(a) Exp 1: historical run

(b) Exp 2: present run with

flood control works

(c) Exp 3: future run with

flood control works

The Lake The Lake

The Lake

(a) (b)

(c)

Wang et al. HSJ 2019 accepted

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Flood risk with flood control measuresat Haihe River Basin, August 1963 flood

Actual inundation area

Assumed inundation area with flood control works

Beijing Beijing

North China

Plain

North China

Plain

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Take home message

• A new discipline of Global Change Hydrology emerges.

• Understanding human-induced impacts to the global water system is the key mission of Global Change Hydrology

• Considerable advances have been made in the past, but more efforts and collaborations are required in order to understand the risks under changing environment and to shape the future of Global Change Hydrology.

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Thank you

http://hydro.igsnrr.ac.cn