24
3.2.5 Conservation Practice (P) Factor
The conservation practice factor (P) was derived based on the land cover map of the
study area (Table 3.3). The conservation practice factor is the relation of soil losses
by an exact practice of crop support, compared with the attitude of straight-line
agriculture up and down the slope. Land use and land cover data (2010), derived
from the European Space Agency Climate Change Initiative Land Cover
(ECACCI-LC) data center. P factor derived from Yang et al. (2003).
3.3 Annual Erosivity Density Ratio
According to Kinnell (2010), the erosivity density coefficient is the ratio of rainfall
erosivity (R) factor to precipitation. In practice, it measures the erosivity per unit of
precipitation (mm) and is expressed as MJ ha
−1
h
−1
.
ED
R
P
=
(3.18)
where ED is the erosivity density, R is the average annual rainfall erosivity, and P is
the average annual precipitation.
3.4 Trend Test
The Mann–Kendall (MK) nonparametric test was used to test for trends in
Kazakhstan. The purpose of the MK test (Kendall 1975; Mann 1945) was to statistically assess the presence of a monotonous upward or downward trend of the variable of interest over time. Annual data series are used to analyze the trends in this
study. The MK test was used in different countries to test the trends in rainfall erosivity (Gedefaw et al. 2018; Gu et al. 2018; Lai et al. 2016; Sadeghi and Hazbavi
2015). The data of individual time series of rainfall erosivity are compared with all
the corresponding data of the time series of the year. Thus, the MK test statistics is
the cumulative result of all data values. Statistics test Mann–Kendall S is equal to
Eq. (3.19)
S
Y Y
i
n
j i
n
i
j
¦ ¦
1
1
1
sgn
(3.19)
The trend test is applied to Y i data values (i = 1, 2, …n − 1) and Y j (j = i + 1, 2, …n).
The data values of Y i are used as reference points for comparison with the data values of Y j which is expressed as follows:
3 Data Sources and Methodology
3.2.5 Conservation Practice (P) Factor
The conservation practice factor (P) was derived based on the land cover map of the
study area (Table 3.3). The conservation practice factor is the relation of soil losses
by an exact practice of crop support, compared with the attitude of straight-line
agriculture up and down the slope. Land use and land cover data (2010), derived
from the European Space Agency Climate Change Initiative Land Cover
(ECACCI-LC) data center. P factor derived from Yang et al. (2003).
3.3 Annual Erosivity Density Ratio
According to Kinnell (2010), the erosivity density coefficient is the ratio of rainfall
erosivity (R) factor to precipitation. In practice, it measures the erosivity per unit of
precipitation (mm) and is expressed as MJ ha
−1
h
−1
.
ED
R
P
=
(3.18)
where ED is the erosivity density, R is the average annual rainfall erosivity, and P is
the average annual precipitation.
3.4 Trend Test
The Mann–Kendall (MK) nonparametric test was used to test for trends in
Kazakhstan. The purpose of the MK test (Kendall 1975; Mann 1945) was to statistically assess the presence of a monotonous upward or downward trend of the variable of interest over time. Annual data series are used to analyze the trends in this
study. The MK test was used in different countries to test the trends in rainfall erosivity (Gedefaw et al. 2018; Gu et al. 2018; Lai et al. 2016; Sadeghi and Hazbavi
2015). The data of individual time series of rainfall erosivity are compared with all
the corresponding data of the time series of the year. Thus, the MK test statistics is
the cumulative result of all data values. Statistics test Mann–Kendall S is equal to
Eq. (3.19)
S
Y Y
i
n
j i
n
i
j
¦ ¦
1
1
1
sgn
(3.19)
The trend test is applied to Y i data values (i = 1, 2, …n − 1) and Y j (j = i + 1, 2, …n).
The data values of Y i are used as reference points for comparison with the data values of Y j which is expressed as follows:
3 Data Sources and Methodology