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Climate and the local water balance

29 important questions on Climate and the local water balance

Getting all properties on soil moisture right, will that give you proper discharge and streamflow dynamics estimation?

No, flux partitioning might be right, but you only look at top 1-2 m of the soil, where further below is also very important

Model that gets evaporation, root zone, etc right, will it get the mean streamflow right?

Yes, it gives a proper indication of average streamflow, but not the dynamics.

How much water leaves the catchment via evaporation vs. Streamflow? Why else is evaporation important for hydrology?

Evaporation 2x the amount of streamflow.
Evaporation changes due to climate change have a large effect on water availability.

Why is recession faster in summer?

--- Min 14 & later: smt with storage and recession being coupled

Name a pro and con for all 5 measurement manners of evapotranspiration

Evaporation pan:
+ Cheap, robust
- Complex relation to actual ET

Lysimeter (cylinder):
+ Accurate, high-resolution
- Expensive, heavy

Catchment water balance:
+ Accurate, large sampling volume
- Temporal resolution: several years (1-5 years), assume no storage change (dS/dt = 0)

Eddy covariance:
+ All ecosystems
- Expensive, footprint definition (measures turbulence, so wind-dependent which can pose a conceptual problem with changing directions and speed, etc.)

Thermal remote sensing:
+ Coverage (global through satellites)
- Land surface temperature is indicative of balance, but not directly related to evaporation

How is evaporation/ET monitored in NL? What's a trend in ET monitoring?

No routine observations by KNMI. They do measure many variables to calculate the potential E.

There's interest in ET monitoring and they sell, but be very critical on their quality!

Name a eddy covariance trend

Global flux towers (FLUXNET) to measure ET. Flux towers are funded to measure carbon exchange and are often in forests/ecosystems.
Thus also be critical of their quality/representation!

Name several trends in long-term soil moisture monitoring networks

Limited, mainly found in agricultural regions (US, Russia, Asia). No global/consistent picture, satellite observations are very shallow.

Mention the main observations/rank the ET rates of bare soil/snow/latitude wise/ET...?

See slide with 4 graphs

Based on what would we partition between transpiration and evaporation?

Transpiration occurs from within plant stomata. Thus the control system is different compared to evaporation (min 42), transpiration has a biological control that might change with climate change.

How does the reduction in ET look like and how should we model this? (min 44)

Non-linear relationship.

Transitional climate: dry summer, wet winters.

!! At low soil moisture, uptake from plant roots can no longer satisfy the atmospheric demand (PET).

!!Important graph on SMC-EF relation: dry-transitional-wet

Stress factor beta

Question on min 60-62 (non)linear relation:
Why do ET linearly decrease over time in drying conditions? How does this relate to different environments?

See Q
Forest: ET decay is slower, vegetation has access to more storage.

Explain the differences between saturated, field capacity, typical and wilting point conditions and how they relate to capilary water?

Saturated: water can move away by gravity water.
Below FC, water is too tightly bound to the soil particles to move by itself.

ADDD

Mention 5 SM metrics, which is most often used?

Absolute water content [mm]
Ratio of saturation or wetness [mm/mm]
Volumetric water content [mm/mm]
SM potential (very non-linear scale!, negative scale means the suction is very strong)
SM index (SMI) [-]

Smt with curvature of water surface, particle size and K

Min 70ish.

Explain power-law/the relation between volumetric water content and unsaturated K? Give also the formula?

Very high exponent, extremely non-linear.
Amount of non-linearity is a function of the soil type

Add formula.

How is field capacity related to SM and Ksat?

- FC is a point between fast drainage and barely any drainage.
- This FC can be seen in time series, e.g. After a few days of drainage.

Why does K increase with increased vol. Water content?

Not sure... Ask?

How does drainage capacity relate to typical range in daily rainfall?

Usually very small part of max Ksat, thus what the soil could transport

What is the soil moisture loss function made up of?

Addition/integration of drainage and ET.

SM does not remain in equilibrium between FC and critical point, why and what is the result?

Because weather is not constant, e.g. it does not rain at constant rate. P and ET are never in balance for a longer period.
Winter: above FC
Summer: decreases to critical SMC or below. It can stay below SMC.

A bimodal state preference (wet and dry end): below critical SMC and above FC.

What is available storage?

The sum of rooting depth and the difference between FC and wilting point.

Typical root depth?

50-100 cm (might be larger for forests)

Why fast response in Cork/wet situation and how is this visible in the graph?

Much wetter/high P and thus a lot of soil moisture and drainage occurring. Drainage values above FC are indicated by sharp peaks
Unless when you have long dry periods, an ET dominated regime could occur.

Faster, bc later slope is much steeper than lsope in beginning. Thus stronger response in drainage than in ET. Drainage responds more non-linear! (see min 99)

Give a short summary of the lecture, use the words: energy limited, water limited, SM, ET, drainage

---

Why is there a horizontal compartment in the loss function?

Not suree?

Explain how an analytical expression for stochastic rainfall can be derived conceptually? Min 100-105.

...

How does climate determine the partitioning of water? --> goal for practical & Min 105-107

Explain the main concepts of the Budyko curve?

Two axis: one with ETpot/P and one with ETact/P based on long term means.

The further you move to the right, you will approach 1 on y-axis: the drier, the more you get to 1.

Humid environment: ETact=ETpot, the more humid, the less likely you'll get below critical SMC.

The question on the page originate from the summary of the following study material:

Catchment and Climate Hydrology

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