Drought
and
Desertification
Mike Kirkby
Water scarcity in space: Southern Tunisia
Xerochore Final Conference: Feb 2010
Murcia: Sept 2009
Mjk: Slide 2
Water scarcity in space: Senegal
Xerochore Final Conference: Feb 2010
Murcia: Sept 2009
Mjk: Slide 3
Bed of the River Ferlo (30,000 km2), N
Senegal, 3 months after the rainy season
Water scarcity in time,
(here seasonal)
Xerochore Final Conference: Feb 2010
MIRAGE startup meeting: Sparti 7-10 March 2009
Mjk: Slide 4
Water scarcity in space and time
• Scarcity in space = aridity
• Scarcity in time = drought
• Scarcity in relation to use
– Camel herding
– Paddy rice
Drought
Xerochore Final Conference: Feb 2010
Desertification
Aridification
What is ‘Desertification’ (UNCCD)
“Desertification" means land degradation in arid, semi-arid and dry subhumid areas resulting from various factors, including climatic variations
and human activities
“Land Degradation" means reduction or loss, in arid, semi-arid and dry subhumid areas, of the biological or economic productivity and complexity
of rain-fed cropland, irrigated cropland, or range, pasture, forest and
woodlands resulting from land uses or from a process or combination of
processes, including processes arising from human activities and
habitation patterns, such as:
•
•
•
(i) soil erosion caused by wind and/or water;
(ii) deterioration of the physical, chemical and biological or economic properties of soil; and
(iii) long-term loss of natural vegetation;
“Combating Desertification" includes activities which are part of the
integrated development of land in arid, semi-arid and dry sub-humid
areas for sustainable development which are aimed at:
•
•
•
(i) prevention and/or reduction of land degradation;
(ii) rehabilitation of partly degraded land; and
(iii) reclamation of desertified land;
Xerochore Final Conference: Feb 2010
Mjk: Slide 6
Annual greening trends 1982-1998 (from Xiao &
Moody, 2005.
Xerochore Final Conference: Feb 2010
Mjk: Slide 7
Mjk: Slide 8
Desertification
and
Development
Climate
Water
Population
density
Agricultural
Potential
Labour
Urban/ Rural
split & Growth
Agricultural demand:
rates
Water, Tractors, Fertiliser
Surplus Energy
production
NonFood surplus
renewable
or deficit
Limited by climate (water), Resources
nutrients and/or
available labour.
Additional labour is needed
to support trade and
Surplus
Without external inputs, converges
industry
labour
on
pastoralism or dry farming
(± water harvesting)
Infra-structure
Includes roads, machinery,
education, healthcare and internal
Tax on GDP
security
Depreciation
Xerochore Final Conference: Feb 2010
Production / Wealth
generation / GDP per capita
Mjk: Slide 9
30
One visualisation of varied climatic regimes
Temp (C)
25
20
15
Rf=PE
Cape Verde
Chania
SE Spain
Montpellier
Yna'an, China
Turkey, Karapinar
Mexico: Acuitzio
SW Portugal
10
5
0
Monthly Rainfall (mm)
-5
0
50
Xerochore Final Conference: Feb 2010
100
Mjk: Slide 10
150
200
Relationships between Pot E-T and mean
monthly temperatures
Pot E-T estimated by Hargreaves’ method from latitude and temperature
Xerochore Final Conference: Feb 2010
*Trondhei
m
1.2
2.9
4.5
6.1
7.8
9.4
11
12
*Tours
*Murcia
Based on CRU 10’ gridded data for Europe, 1901-2000
Izmir*
Months
with
Precip’n
< 0.6 x PE
in an
average
year
Ephemerality:
Monthly runoff is accumulated downstream to give continuity of flow in
terms of rainfall and geology, with estimated Actual E-T and Runoff.
ephemerality
Low
High
country polygon
Annual precipitation 1901-2000
Xerochore Final Conference: Feb 2010
Rainfall & Pot-ET for 4 sites across Europe
Based on CRU 10’ gridded data for Europe, 1901-2000
Trondheim
Tours
Murcia
Xerochore Final Conference: Feb 2010
Izmir
Environmental impacts of drought ?
• Rainfall or runoff ?
• Single month/year or cumulative effect ?
• Desertification impacts ?
– Wind erosion and Fire
• Vegetation as a key intermediary
– Salinisation
• Mainly produced by long term aridity
– Water erosion
• Mainly produced by floods rather than droughts
Xerochore Final Conference: Feb 2010
Rainfall into Runoff ?
Precipitation
Potential
E-T
Infiltration
Actual E-T
GPP
Soil moisture
Vegetation
biomass
Respiration
Drainage
Xerochore Final Conference: Feb 2010
Leaf fall etc.
Cumulative anomalies for Precipitation and Runoff,
and estimated uncultivated biomass: Murcia data
Range / average mean
For precip’n =4.3 yrs
For runoff = 10.9 yrs
Coeff of variation = 14.1%
Xerochore Final Conference: Feb 2010
Estimated biomass and variability: 1901-2000
Biomass plotted on log scales: cv=coefficient of variation = SD/Mean
Xerochore Final Conference: Feb 2010
1.0%
2.2%
4.0%
6.2%
9.0%
12.2%
16%
20.2%
25%
Coefficient
of
Variation
in monthly
‘biomass’
for 19012000
Based on CRU 10’ gridded data for Europe, 1901-2000
Modelling Wind Disturbance at the soil surface
Soil
moisture
+
Surface
grain size
+
Critical near
surface shear stress
for disturbance
+
Xerochore Final Conference: Feb 2010
Vegetation
biomass
+
Distribution
of 2m wind
speeds
Aerodynamic
roughness
+
Frequency of
Critical
wind
2m wind
disturbance
at
speed
surface
Modelling wildfires in each month
No of days
with >3mm
rain
Lightning
frequency
Max daily
temperature
+
+
+
Fire Danger
Index
Moisture
content of
Xerochore Final Conference:Vegetatio
Feb 2010
n
+
No of
ignition
events +
+
Rate of fire spread
+
Vegetatio
n biomass
Visitor
numbers
Mean
wind speed
+
Expected
Burn area
Wildfire burns and climate
Frequency
Ignition
Fuel load in
each fire
Combined
effect
Mean annual precip’n
Xerochore Final Conference: Feb 2010
Cumulative runoff anomalies, 1901-2000
Xerochore Final Conference: Feb 2010
Runoff
= Precip – Act ET: Time is number of years storage required to buffer observed range
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Number of
Years
storage
needed for
runoff
anomalies
1901-2000
Based on CRU 10’ gridded data for Europe, 1901-2000
Xerochore Final Conference: Feb 2010
Mjk: Slide 26
•Ideally a benign positive
feedback, leading to
exponential growth of GDP
•Small labour surplus
supports trade, wealth
supports more productive
farming and so on.
•Kick-started by resource
wealth or a coastal location
•Hindered by low rainfall
and population, or a landlocked location
•Once started, feedback may be cut in various ways, e.g.
•Conflicts that destroy production and absorb person power.
•Diversion of GDP from useful infrastructure (the Pyramids or Foreign debt)
•Over-dependence on rigid technical infrastructure (irrigation and salinity; US auto
industry) without alternative investment
•External exploitation without local investment
Xerochore Final Conference: Feb 2010
Mjk: Slide 27
Mitigating desertification ?
•Physical remedies that increase
productivity
•Terracing, mulching, intercropping….
•Investment in infrastructure
Roads, wells, machinery, healthcare,
education
Supporting trade & improving
agriculture
•Providing (cheap & renewable) energy
Increasing productivity and releasing
labour
•Others, e.g.
•Migration, Exploit resources
Xerochore Final Conference: Feb 2010
Mjk: Slide 28
Possible responses to external drivers
Reduced aid to developing countries
Financial meltdown &
Economic recession
Expansion of Bio-fuel
production
Global warming
Limited investment in new
technologies
Expansion of cropping on
marginal land
Need to
reduce
emissions
Acceleration of
forest
destruction
Shift toward
radical
technologies
Land degradation
Xerochore Final Conference: Feb 2010
Mjk: Slide 29