tailieunhanh - Modeling Hydrologic Change: Statistical Methods - Chapter 8

Phát hiện thay đổi trong khoảnh khắc Biến thủy văn phụ thuộc vào nhiều yếu tố liên quan đến các quá trình khí tượng và thủy văn chi phối hành vi của họ. Các giá trị đo thường được điều trị như các biến ngẫu nhiên, xác suất xảy ra của tất cả các biến ngẫu nhiên được mô tả bởi phân phối xác suất cơ bản, trong đó bao gồm cả các thông số và chức năng. Thay đổi hoặc là khí tượng hoặc các quá trình thủy văn có thể gây ra thay đổi trong dân số cơ bản. | 8 Detection of Change in Moments INTRODUCTION Hydrologic variables depend on many factors associated with the meteorological and hydrologic processes that govern their behavior. The measured values are often treated as random variables and the probability of occurrence of all random variables is described by the underlying probability distribution which includes both the parameters and the function. Change in either the meteorological or the hydrologic processes can induce change in the underlying population through either a change in the probability function or the parameters of the function. A sequential series of hydrologic data that has been affected by watershed change is considered nonstationary. Some statistical methods are most sensitive to changes in the moments most noticeably the mean and variance other statistical methods are more sensitive to change in the distribution of the hydrologic variable. Selecting a statistical test that is most sensitive to detecting a difference in means when the change in the hydrologic process primarily caused a change in distribution may lead to the conclusion that hydrologic change did not occur. It is important to hypothesize the most likely effect of the hydrologic change on the measured hydrologic data so that the most appropriate statistical test can be selected. Where the nature of the change to the hydrologic data is uncertain it may be prudent to subject the data to tests that are sensitive to different types of change to decide whether the change in the hydrologic processes caused a noticeable change in the measured data. In this chapter tests that are sensitive to changes in moments are introduced. In the next chapter tests that are appropriate for detecting change in the underlying probability function are introduced. All of the tests follow the same six steps of hypothesis testing see Chapter 3 but because of differences in their sensitivities the user should be discriminating in the selection of a test. .