Transcript Morning Plenary Presentation - Martin Todd: CC impacts on recharge

Understanding climate impacts on
Groundwater
Martin Todd, University of Sussex
[email protected]
GroFutures: Groundwater Futures in Sub-Saharan Africa. UpGro Consortium grant 2015-19
Context: Africa is changing rapidly and demand
for fresh water will increase
• e.g. Intensified agriculture.
e.g. Demand for piped
water in rapidly
growing urban centres
How might the global water cycle respond
to a warmer climate?
% change in water
vapour with
warming
Heavy rainfall may follow
C-C relation 7% per
degree warming
% change in global
mean precipitation
with warming
Global average
precipitation ~3%
increase per degree C
warming
Allen and Ingram (2002) Nature
Spatial pattern of change in precipitation is highly
variable and uncertain
Pattern reflects ‘wet get wetter’ vs ‘warmest get wetter’ and
other changes to atmospheric circulation
(Stippled dots show where change is bigger than internal variability, hatching
where change is less than internal variability)
Climate impacts on groundwater: a
neglected issue?
• Groundwater – climate change impact studies lag behind
those for surface hydrology
– ‘Both detection of changes in groundwater systems and
attribution of those changes to climatic changes are
rare owing to a lack of appropriate observation wells
and a small number of studies’
– ‘the relation between groundwater and climate change
was rarely investigated before 2007’
• (IPCC AR5 WG2, 2014)
Improving our understanding: GroFutures will
establish a Network of African Groundwater
Observatories
• Long term data: many
decades
• Cover the primary
hydrogeological and
developmental
contexts
Initial case study
Semi-arid Tanzania
(In weathered
crystalline rock
environments that
underlie 40% of
sub-Saharan Africa
Case study: Episodic recharge at Makutapora in
semi-arid Tanzania
Provides the longest, published record of
groundwater levels anywhere in the tropics
Makutapora wellfield Highly nonsupplies capital city
linear rainfallDodoma
recharge
relationship
Recharge occurs
only 1 year in 5
Taylor et al. (2013) Nature Climate Change 3: 374-378.
Episodic groundwater recharge events linked
to global pattern of climate variability
Sub-continent wide pattern of
rainfall anomalies associated with
the 7 largest GW recharge events
Timeseries of this rainfall pattern
related to ENSO and Indian
Ocean Dipole pattern
Taylor et al. (2013) Nature Climate Change 3: 374-378.
Recharge futures?
Central Tanzania, 2070-99
• Projected increase
in seasonal
extreme rainfall is
greater than for the
mean
• This may favour
GW recharge
Spread of projected percentage
change in mean (left) and 90th
percentile rainfall (right) in IPCC
AR5 models
Taylor et al. (2013) Nature Climate Change 3: 374-378.
Projected climate change impacts on recharge
• Large-scale models
project a very mixed
and uncertain picture
e.g. WaterGAP: Portmann et al. (2013) Environ. Res. Lett. 8: 024023.
Confronting the model world with the real world
WaterGap model
Observations in Africa reveal recharge pathways
(focused, non-matrix) completely divorced from
models commonly used to estimate recharge
Makutapora observations
Jules model
Is this non-linear relationship
observed at a few locations
in the tropical Africa
widespread?
Good simulation occurs ‘by chance’ as JULES does
not have explicit groundwater recharge process
Summary of GroFutures activities
• Data: NAGO network of study sites. High quality, long-term
data
• Process understanding: Rainfall-recharge realtionships and
recharge pathways
• Models: Improve GW models at study sites
• Future Projections of GW resource: Based on climate and
socio-economic developmental scenarios
• GW management and decision-making: Apply ‘pathways’
approach to inform sustainable and ‘pro-poor’ GW
development.
GroFutures Pathways Approach
• Pathways analysis rooted in extensive, multi-level stakeholder
engagement and multi-criteria mapping
• ‘Open up’ range of GW development pathways: bush
paths/motorways
• Evaluate viability and sustainability of identified pathways
Conclusions
• Rapid development in Africa will inevitably result
in substantial increases in demand for freshwater
• Sustainable development requires improved
understanding of the resource
– Initial analysis indicates the need for long term data
across Africa
– Model development
• Pro-poor GW management
• GroFutures hopes to address these issues