a pan-african inter-comparison of the relationship...
TRANSCRIPT
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groundwater-fed irrigation (Zambia)
Richard Taylor (UCL Geography) on behalf of The Chronicles Consortium
A pan-African inter-comparison of the relationship
between precipitation and groundwater recharge from
in-situ observations and large-scale models
JpGU-AGU Joint Meeting, M-ZZ40: Sustainable global groundwater management for human security, 22 May 2017
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artesian borehole, Singida (central Tanzania)
“Climate change is projected to reduce renewable… groundwater resources significantly in most dry subtropical regions (robust evidence, high agreement).”
IPCC WGII (2014) Chapter 3, page 232
“The uncertainties in projected groundwater recharge that originate in the hydrological models have not yet been explored.” IPCC WGII (2014) Chapter 3, page 244
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IAH/UNESCO-IHP: The Chronicles ConsortiumAbiye, Tamiru (University of Witswatersand, South Africa)
Ayenew, Tenalem (Addis Ababa University, Ethiopia)
Boukari, Moussa (Université d'Abomey Calavi, Benin)
Cuthbert, Mark (Cardiff University , UK)
Döll, Petra (Goethe-University Frankfurt, Germany)
Favreau, Guillaume (IRD, France)
Goni, Ibrahim (University of Maiduguri, Nigeria)
Jasechko, Scott (University of Calgary, Canada)
Kashaigili, Japhet (Sokoine University of Agriculture, Tanzania)
Kim, Hyungjun (University of Tokyo, Japan)
Kotchoni, Valerie (Université d'Abomey Calavi, Benin)
Koussoubé, Youssouf (Université d’Ouagadougou, Burkina Faso)
Lawson, Fabrice (Université d'Abomey Calavi, Benin)
Lo, Min-Hui (National Taiwan University, Taiwan)
MacDonald, Alan (BGS, UK)
Müller Schmied, Hannes (Goethe-University Frankfurt, Germany)
Nazoumou, Yahaya (Université Abdou Moumouni, Niger)
Nyenje, Philip (Makerere University, Uganda)
Oki, Taikan (University of Tokyo, Japan)
Owor, Michael (Makerere University, Uganda)
Rodell, Matthew (NASA, USA)
Scanlon, Bridget (University of Texas, USA)
Shamsudduha, Mohammad (UCL, UK)
Sibanda, Tenant (World Vision, Zimbabwe)
Sorensen, James (BGS, UK)
Taylor, Richard (UCL, UK)
Tindimugaya, Callist (MWE, Uganda)
Todd, Martin (University of Sussex, UK)
Villholth, Karen (IWMI, South Africa)
Vouillamoz, Jean-Michel (IRD, France)
Wada, Yoshihide (IIASA, Austria)
and growing… join us?
Sokoine University of Agriculture (Tanzania): 9-12 February, 2017
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• uncertainty in the
magnitude and
distribution of
modelled recharge
is substantial -
mean annual
recharge
subsurface runoff
(SSR) &
groundwater
recharge (GWR)
from 1980-2014
Inter-comparison of 4 GLDAS LSMs & 5 GHMs
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modelled recharge by climate zone
CGIAR Aridity Index
• uncertainty in
simulated recharge
increases in semi-arid
regions
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observations in seasonally humid Benin(a) Cococodji
(b) Allansakomey
(c) Natitingou
7
6
5
4
3
2
1
0
200
160
120
80
40
0
data
model
rainfall
0 2 4 6 8
Observed WTD (m)
0
2
4
6
8
Data
y = 0.98 x(R² = 0.70)
17
16
15
14
13
12
200
160
120
80
40
0
data
model
rainfall
10 12 14 16 18 20
Observed WTD (m)
10
12
14
16
18
20
Data
y = x(R² = 0.81)
20
16
12
8
4
0
100
80
60
40
20
0
data
model
rainfall
0 4 8 12 16 20
Observed WTD (m)
0
4
8
12
16
20
Data
y = 0.98 x(R² = 0.6)
• GW levels well
simulated using
scalar recharge
model of precip
exceeding a
threshold (5 to 15
mm·day-1) & short
lag times
• apparent precip
threshold of ~ 200
mm·year-1 for
recharge to occur
• rapid responses to rainfall inconsistent with a Darcy-Richards
representation of unsaturated zone flow, implying bypass flow
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observations vs. models in humid Benin
Kotchoni et al. (in review) Hydrogeol. J.
1994 to 2015
• observed and simulated relationships between precipitation & diffuse
recharge in humid areas (e.g. Benin, Uganda) compare favourably
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recharge observations in semi-arid Niger
• diffuse recharge model proves inadequate; focused recharge
pathway is evident from groundwater-level observations
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ephemeral stream flow in central Tanzania during 2015-16 El Niño
recharge observations in semi-arid Tanzania
• recharge occurs episodically (El Niño) and strongly correlated to the
duration of ephemeral stream discharge (i.e. focused recharge)
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Taylor et al. (2013) Nat. Clim. Change 3, 374-378.
• observed non-linear relationship between precipitation & recharge
not well represented in models based on diffuse recharge pathways
models/observations in semi-arid Tanzania
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models/observations in semi-arid South Africa
• observations clearly reveal substantial, episodic recharge events but
these are not well represented in most large-scale models
Limpopo Basin: a selection of DWAF records
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Preliminary results from the inter-comparison:
• substantial uncertainty exists in recharge modelled by 4 GLDAS
LSMs (subsurface runoff) & 5 GHMs
• modelled and observed relationships between precipitation &
diffuse recharge in humid areas are comparable – rapid water-
table responses inconsistent with Darcy-Richards soil-zone flow
• observations across Africa indicate a bias in recharge to heavy
rainfall events (daily to seasonal) via pathways (i.e. soil
macropores, focused) not currently represented in models
• models are inconsistent with observed recharge in semi-arid
environments - models do not represent focused recharge,
the primary pathway by which recharge is observed to occur
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Thanks for listening!
Victoria Falls