Jared Ostendorf

Jared Ostendorf

October 9, 2006

Exercise 2

Task 1

Monthly meteorological data for Pahang Tenggara, Malaysia.
Month / Rainfall (inches) / de (Hg) / Edt / P-Edt / Mt-1 / Mt(1) / Runoff/Vertical Drainage / Soil Water Store
5.00
1 / 7.3 / 0.49 / 5.91 / 1.39 / 5.00 / 6.39 / 1.39 / 5
2 / 7.7 / 0.51 / 6.13 / 1.59 / 5.00 / 6.59 / 1.59 / 5
3 / 9.0 / 0.59 / 6.94 / 2.05 / 5.00 / 7.05 / 2.05 / 5
4 / 8.7 / 0.59 / 6.88 / 1.87 / 5.00 / 6.87 / 1.87 / 5
5 / 8.2 / 0.55 / 6.46 / 1.74 / 5.00 / 6.74 / 1.74 / 5
6 / 5.1 / 0.53 / 6.34 / -1.19 / 5.00 / 3.81 / 0.00 / 3.81
7 / 5.8 / 0.53 / 6.29 / -0.54 / 3.81 / 3.27 / 0.00 / 3.27
8 / 6.7 / 0.53 / 6.31 / 0.42 / 3.27 / 3.69 / 0.00 / 3.69
9 / 7.7 / 0.55 / 6.46 / 1.19 / 3.69 / 4.88 / 0.00 / 4.88
10 / 12.6 / 0.50 / 6.01 / 6.60 / 4.88 / 11.48 / 6.48 / 5.00
11 / 13.6 / 0.40 / 5.02 / 8.55 / 5.00 / 13.55 / 8.55 / 5.00
12 / 13.1 / 0.37 / 4.71 / 8.43 / 13.43 / 8.43 / 5.00

Why de instead of pan ev?

Answer:During the months of June, July, August, and September, the soil water storage never meets the storage capacity. During these months, this area does not get as much precipitation and the area of Pahang Tenggara in Malaysia should be concerned with the smaller amounts of water in the soils. Not only is the precipitation low during these months, but the evaporation is still high so there is minimal if any runoff. October, November, and December get a lot of precipitation. This recharges the soil water content to its full capacity. With low evaporation during these months and probably a higher rate of precipitation, there are large amounts of runoff and vertical drainage. Pahang Tenggara should be concerned with these large amounts of runoff if they come in quick stages and at high velocities because it could cause flooding in low areas. During the first five months of the year, it is important to notice there is about average rainfall during these months throughout the whole year. There is enough rainfall to keep the soil content at its maximum value. The evaporation is high causing there to be smaller amounts of runoff.

These graphs depict a monsoonal season. Their dry months are in June, July, August, and September while their wet months are in October, November, and December. During these wet months, they must get a lot of consistent rainfall with the runoff ratios being so high.

Two monsoonal seasons in Malaysia because any wind direction carries a lot of water vapor over the ocean to this islands.

Assumptions:

No vertical or surface runoff until soil water overflows over the bucket. In reality, most watersheds are leaky, which means that we have quite a mount of streamflow even during dry seasons.

AET is equal to pan evaporation. But, in fact AET is lower than pan evaporation in most seasons maily because of the shortage of soil water supply.

For the check of mass conservation, you have to calculate input-output of the whole period and compare it to the increase of soil water store.

1.0/3

Task 2-1

Mean= 999.0872 mm You are plotting annual discharge, not annual RR.

Standard Deviation = 307.3158 mm

Ratio=307.3158:999.0872

The ratio of standard deviation to mean is called a coefficient of variation, which represents the relative variation of a variation, normalized by its magnitude.

0.5/2

Task 2-2

Answer:As the annual precipitation increases, the runoff ratio increases as well. Again. You plot annual discharge, not annual runoff ratios. And, why don't you plot annual runoff ratios against annual precipitaiton?For example, in the graph above, the two shapes of the data are very similar; however, the runoff ratio is smaller than the precipitation throughout time. This makes sense because if there was not any precipitation, there could not be any runoff. The runoff ratio increases due to either of two scenarios: 1) the precipitation was falling at too quick of a rate for it to infiltrate into the soil, thus causing runoff or 2) the soil had already reached its infiltration capacity in which the soil was saturated. It would not make sense for the runoff ratio to get larger if the precipitation was smaller because smaller amounts of precipitation would either infiltrate into the soil or have a smaller runoff ratio. Precipitation is always greater or equal to runoff (equal being when the soil is already saturated).

Consider the effects of soil water content on the generation of surface runoff. As precipitation increases, soils tend to be wetter, which means the decline of infiltration capacity. As a result, more portion of precipitation flows out as surface runoff without infiltrating into soils.

0.5/2

Task 2-3

AnswerAfter looking at the data above, annual runoff ratios cannot be an intrinsic hydrologic property of a watershed. Last class we learned that static quantitative data are fixed variables for individual and cumulative watersheds. In the case of our runoff ratios, runoff is dependent on precipitation, its flow rate, and the soil capacity. Runoff is not static because the amount is not controlled and varies over time. The flow rate also varies over time. In the case of the soil property, the runoff is dependent on how much water is in the soil and whether it has reached its capacity (saturation) or not. The only way a watershed could have a static runoff ratio is if the soil water content was controlled, the flow rate was controlled, and the precipitation was controlled. This watershed being described would have to be human made without the variables of nature taking its course. Your argument goes too far. In brief, the inter-annual variation of runoff ratios is high because it is strongly correlated with the hydroclimatic condition of a year.

2/2

Task 2-4

Answer:The statement that the water budget equation of WS 18 can be simplified so that the annual actual evapotranspiration of the watershed may be approximated to (annual precipitation-annual stream discharge) is wrong. When someone only takes into account the annual precipitation-annual stream discharge, they are ignoring what happens when infiltration takes place. Infiltration taking place could cause the actual evapotranspiration to be less than if no infiltration takes place at all. Nope. A weir to measure stream discharge is designed to eventually capture infiltrated water. When precipitation falls to the soil, it can pond, infiltrate, or runoff depending on precipitation flow rate, precipitation amount, soil water capacity, etc. With this being said, if water infiltrates into the ground, less water has the potential to evaporate. The simplification of the water budget equation does not include the vegetation’s uptake of the water by the roots. Pressure between the soil and roots causes them to bring up water to the surface.

Since the area has a deep weathered saprolite underground structure, we expect there is significant deep groundwater flow, bypassing a weir to measure stream discharge. So, in reality, AET can be much lower than P-Q.

2/3

Task 3 Effects of Climatic Change on Runoff

Percentage Change in Runoff, q

Runoff Ratio, w^Evapotranspiration % Increase

Answer:The relative increase of runoff of the Coweeta basin when the precipitation increases by 20% and evapotranspiration increases by 10% is 125%.

More exactly,

so the relative increase of runoff is 29.9%.

3/3

Task 4

Answer:GRACE’s five year mission is “to produce the most accurate map of Earth’s gravity every made and to reveal how it changes over time.” With having two satellites just 220 kilometers apart on the same path, GRACE is able to measure the distance between the two satellites as Earth’s gravity changes. Since mass transportation is key in the changing gravity in different parts of the earth, GRACE is able to track where the mass (be it water, magma, land, etc) increases and decreases. GRACE will enable the oceanographers to get the to deep ocean currents. Mass water movement affects the climate of the entire Earth. The article points out that “Gravity measurements have an advantage over standard measurements of sea level or polar ice volume, in that they can distinguish expansion due to heating from an influx of water.” Most importantly in our discussions, GRACE enables scientists to track changes in soil moisture. Soil moisture is an important part of the “hydrological cycle that influences climate change, erosion, reservoir management, water quality, and ecology.” In short, they will be able to track the masses of water over time because of the changes in gravity. Together with other data obtained on Earth (such as when it rains, temperature changes in glacier regions, droughts, etc.) geographers can make accurate decisions as to the effects of these processes. In using GRACE, it is a more precise way to measure soil moisture, runoff, and evapotranspiration with the new satellites.

With having the data of the current soil moisture in a given area, people will have more time to plan for droughts. They will be able to see how deep the water goes into the ground and calculate whether the roots of the vegetation have an adequate water supply. Also, the amount of the water supply or soil moisture in a given area will be more precise instead of depending on estimations based from region to region. In addition, with knowing the deeper water currents in the oceans that significantly impact the climate, people can plan for precipitation levels in advance. Whether it be moderate precipitation levels people are dependent on for vegetation growth or extreme levels where they would have to prepare for flooding, GRACE would allow them to be ready for the conditions to come.Good points.

And, Using a water balance equation, we can estimate ET of the whole river basin.

3/3

Total:

12/18= / 6.7