L2 and 3

Question 1

what are the major components of the water cycle

Answer 1

• precipitation: P, rain or snow
• (evapo)transpiration: ET. evaporation is the conversion of water from liquid to gas from the earth’s surface. transpiration is the evaporation of water through the leaves of plants
• runoff: surface + sub surface runoff. surface runoff is the flow of water that occurs when excess precipitation or meltwater over the land surface flows. subsurface runoff is the waterflow within the saturated soil
• storage: in atmosphere, on surface, and in ground (soil+aquifer)

Question 2

water balance equation

Answer 2

P = R + ET +- dS
R = P- ET +-dS

Question 3

what is the global water cycle

Answer 3

water moves from one reservoir to another (atmosphere, ice, fresh/salt water, ground). this circulates naturally and this is the water cycle

Question 4

water resource availability depends on:

Answer 4

1. how much water is in each storage
2. when and how fast water moves through the system
3. how much water we use
4. how clean the water is

Question 5

what are the main water use sectors

Answer 5

Irrigation/agriculture (70% globally)
domestic water use (11%)
industrial water use (19%)

Question 6

driving factors behind water use in irrigation

Answer 6

• the size of the area that needs to be irrigated
• crop water requirements (soil moisture high? crop needs less water)

Question 7

driving factors behind water use in the domestic sector

Answer 7

• size of population
• economic development
• domestic water use intensity

Question 8

driving factors behind water use in the industry

Answer 8

• economic development
• population density
• manufacturing water use intensity

Question 9

what are drivers of change in global water resources availability

Answer 9

• socio economic development: population growth so an increase in food/energy/resourcce demands and an increase in sectoral water use. economic development and land use changes
• climate change: the water use for irrigation, domestic use and industry will increase on a global scale

Question 10

why is there an increasing pressure on our freshwater resources?

Answer 10

• more evaporation due to warmer temperatures, thus the irrigation demand is higher
• excessive water withdrawals in large parts of the world
• groundwater withdrawals –> groundwater depletion happens more in intensively irrigated areas in dryer climates. groundwater depletion is the permanent loss of groundwater from its storage and has more than tripled in the past decade. in the current climate conditions, not all aquifers are recharged

Question 11

how does CC impact global water availability

Answer 11

mainly by changes in spatial and temporal patterns of precipitation and evaporation.
the longest increase in terrestial precipitation are in the high northern latitude and in the tropics. precipitation and evaporation decreases in S america mediterranean, and S africa. if theres less precipitation there’s also less water available to evaporate. overall decrease in precipitation –> dryer soil. hihger temperature, more evapotranspiration, more runoff, less soil moisture

Question 12

why use large-scale hydrological models?

Answer 12

1. to understand global processes and interactions, e.g. the impacts of CC on water resources availability on a global scale
2. to make estimates of water resources availablity now, and in the future. by understanding - current and past trends and anomalies to better predict the future - long term future trends (through scenarios) - forecasting.

overall aim: better water resources management worldwide

Question 13

what do large-scale hydrological models simulate and what are they used for?

Answer 13

the water cycle and the water balance equation. they are used to
- quantify water resources
- predict floods/droughts
- evaluate cc/land use change impacts
- monitor water quality

Question 14

VIC WUR model. general characteristics,

Answer 14

vertical infiltration capacity model
- includes the water and energy balance
- accounts for evapotranspiration
-simulates river discharge
- distributed, 50x50 km grid cells
distinguishes 3 soil layers, it accounts for soil moisture content
- human water use is being implemented

Question 15

VIC WUR model. input and output

Answer 15

input
- hydrological drivers
parametarization
- soil
- land cover/vegetation
- elevation
- flow direction
- reservoirs
- water demands per sector
- aquifer parameters

output:
- river discharge
- soil moisture
- snowmelt
- evapotranspiration
- water uses per sector and return flow
- water table depths, groundwater flow

Question 16

how can large-scale hydrological models be used for the global assessments of water stress?

Answer 16

they can model how much water is available and how much water is used. models global processes and interactions and its effect on water resources. you can model the impact of cc on water resources availability or model the waterstress on a global level. you can make forecasts and do scenario analysis. in short: you can model water availability and water withdrawal. together this is an indicator for water stress

Question 17

challenges in global scale hydrological modelling

Answer 17

• how to model climate forcing - this is dependent on climate data and climate scenarios from global climate models
• parametarization - depends on data availability and quality, on model resolution and heterogeneity and complexity
• uncertainties - depends on the computational challenges, the scale of the model and on how to evaluate uncertainties

Question 18

what is needed to simulate CC impacts on water resources availability with large-scale hydrological models?

Answer 18

you need emission scenarios (e.g. RCPs), climate models, climate scenarios, an impact model (e.g VIC), and projections. the results of multiple global climate models are used to assess the impacts of cc on the availability of water resources