Task 1. Calculate monthly stream discharge of WS17 when the watershed was no32 t
33 disturbed.
Q1. Below is the image which depicts the linear regression line over the monthly stream flow data of WS17 and WS18.
Figure1. Linear regression line over the monthly stream flow data of WS17 and WS18.
From the line, we can get the value of the coefficients a and b:, andR2=0.9971, the coefficient of determination is quite close to 1, and it indicates that the two data sets have a strong linear relationship. The equation fits the monthly stream discharge data well. The linear relationship is valid.
Overall, the linear regression line fits the observed data well, but the coefficients of the regression line are determined dominantly by high flow data. As a result, this graph shows a systematic bias for low flow less than 50 mm/month. The bias can introduce serious errors in calculating monthly stream discharge of undisturbed WS17 during dry season.
3/3
We can calculate the monthly stream discharge of WS17 for the entire data collection period in the Excel file: coweeta_monthly.xls. The data is located in D2:D781.
Q2: I think the assumption is acceptable. Because if WS17 are not disturbed, this watershed should have the same forest type as WS18, and the two watersheds may have nearly the same soil type, climate, for the two watersheds are near to each other. We can think that the environment of the two watersheds is quite similar. Therefore, we can derive the assumption.
The potential error sources may include the following:
1)The spatial variability of precipitation in the two watersheds; No. the watersheds are too small.
2)The difference between the forest type in the two watersheds, such as density, forest age and so on; Once canopy is closed, stable.
3)The topographyvariability in the two watersheds; Almost the same.
4)The soil type, biomass, climate variability in the two watersheds;
5)The climate has continuously changed through the years, for example, the mean temperature, the carbon budget and other factors may change with time. It is possible that in a few years, the two monthly stream discharge have a linear relationship which has a parameter set of A. In the next a few years, the two monthly stream discharge have a linear relationship which has a parameter set of B. Though the monthly stream discharges in the two different periods both have linear relationship, the detailed parameters may vary. This can result in error.
The range of monthly stream flow for the undisturbed period does not cover the range of the entire data collection period. Therefore, there is a possibility that the regression relationship derived from the 3 year data does not represent well the relationship of the two watersheds, particularly when they experience extreme climate conditions, such as hurricanes or severe droughts.
If natural disturbance such as hurricanes or insect infection influences the hydrologic response of one of the two watersheds after the clear-cutting, the derived regression relationship is no longer valid. In fact, the hemlock trees of WS18 were seriously infected by the introduction of hemlock woolly adelgid (Adelges tsugae), an exotic invasive insect, in 2002 (
1.5/2
Task2. Evaluate the effects of clear-cutting and plant plantation on the annualwater yield of WS17.
Q3: Below is the image which depicts the difference of two annual stream discharges to show the change of annual water yields caused by the land cover disturbance.
Figure2 Difference of discharges between two mechanisms of WS17
Put a horizontal line at Y=0 to clearly show the signs of difference. 3/3
Q4 After the clear-cutting in 1940, the undisturbedannual stream discharge is much less than the actual annual stream discharges of WS17. This phenomenon means that with the forest and vegetation, the soil can hold more water in the soil profile and increase the available water content, and also can increase infiltration rate. Do you mean macropores? Therefore, the surface runoff is reduced and the stream flow is reduced with the same precipitation. The clear-cutting eliminated the evaporation from intercepted rainfall, and reduces transpiration rate from vegetation.
In 1972, the annual water yields would stabilize. It took 17 years to reach the stable state. During the transient period,the annual water yields gradually reduced and finally reached a stable state, the actualWS18 annual water yields has a substantial decrease of about 200 mm than the undisturbed WS18 annual water yields from 1972.
From the paper “Swank, W.T. & Douglass, J.E. (1974), Streamflow greatly reduced by convertingdeciduous hardwood stands to pine, Science 185(4154), 857-859.”I know that with the growth of the white pine,the stream flow or the surface runoff is reduced. When the white pines trees gradually grew, they began to hold water trees not hold water but absorb and transpire soil water through their roots and increase infiltration and evaporation, the stream flow gradually reduced until the white pine trees are fully mature and the stream flow reached a relatively value. And the stream flow in the white pines forest is less than deciduous hardwood because the evaporation is higher. Su. You are talking about only infiltration, but infiltration is not the main process affected by clear-cutting.
Gradual decrease of annual water yields of WS17 after 1960 because once white pines are established, the canopy area expanded very rapidly as they grew.
2/4
Q5: The evaporation rate of mature pine forest is higher than that of mature deciduous oak forest.Because the stream flows in white pine forest is less than that of deciduous oak forest. According to the water budget equation: AΣPΔt=S+ΔD+ΔM+Uv+Uh+AΣEΔt. From the equation, the precipitation of WS17 will not change much regardless the type of forest. In one water year, ΔD and ΔM can be regarded as zero. Surface runoff is controlled by precipitation and evaporation.
Because the LAI in a hardwood stand is greatly reduced by leaf fall and white pine do not have leaf fall in dormant season, then the interception and subsequent evaporation of rainfall is greater than for pine than hard woods during the dormant season. The result is white pine forest has much less stream flow. More effective leaf structure of coniferous forest for ET than deciduous tree. And, broader leaf area of coniferous even during summer. 2/3
Task3. Evaluate the effects of clear-cutting and plant plantation on the seasonal water yields of WS17.
Q6: Below is the image which depicts the difference in Monthly stream discharge of undisturbed WS17 and disturbed WS17.
Figure3 Difference in Monthly stream discharge of undisturbed and disturbed WS17 Correct.
From the picture, we can see that in winter (Nov, Dec, Jan) and late spring (Apr, May), the difference is relatively high. And in early spring and summer as well as fall, the difference is low. From the reference paper, the reason is that in dormant season (winter), LAI in a hardwood stand is greatly reduced by leaf fall, and LAI is related with interception loss, therefore, white pine trees have much higher interception and evaporation in winter and the stream flow is then reduced.
Because in late spring, the hardwood stand is leafing out and on the other hand, the pine is in full leaf. Stronger solar radiation during spring increases ET, which makes the difference larger. The difference in LAI is also great, which results in the high difference in stream flow in late spring..
From what mentioned above, the conclusion is that the difference in stream flow results from the interception and evaporation rate of the two forest types. Due to the difference in LAI of hardwood and pine, the interception and evaporation rate is also different. Good. 4/4
Total:
15/19= / 7.91