Climate overtakes vegetation greening in regulating spatiotemporal patterns of soil moisture in arid Central Asia in recent 35 years

Figures & data

Figure 1. Study area.

Table 1. Summary of the datasets used in the analysis.

Data	Source	Temporal resolution	Spatial resolution	Available period of product
NDVI	NOAA CDR AVHRR NDVI V5	Monthly	5 km	1981–2020
LAI	GLOBMAP LAI V3	Half month, 8-day	0.073°	1981–2020
Soil moisture	(Jiang et al. 2019); CCI Passive V6.1	Daily	9 km; 0.25°	1978–2020
Precipitation & Temperature	CRU	monthly	0.5°	1901–2020
Land cover	CAS Earth	every 5-years	30 m	1985–2020

Table 2. Classification of NDVI, LAI and soil moisture trends.

β	Z value	Trend of NDVI (LAI)	Trend of soil moisture
<−0.0005	<−1.96	Severely degraded	Severely drying
<−0.0005	−1.96~1.96	Slightly degraded	Slightly drying
−0.0005~0.0005	−1.96~1.96	Stable	Stable
≥0.0005	−1.96~1.96	Slightly improved	Slightly wetting
≥0.0005	≥1.96	Significantly improved	Significantly wetting

Figure 2. Spatial distribution of turning years: NDVI (a), LAI (b), soil moisture (c), and the columnar diagram of the area proportion of each turning year (d). Blank areas indicate no turning year (P > 0.05).

Figure 3. Spatial distribution of the trend classes for NDVI (a), LAI (b) and soil moisture (c) from 1985 to 2020 in Central Asia.

Figure 4. Partial correlation coefficients (Rp) between soil moisture and the following variables: (a) NDVI (removing the effects of precipitation and temperature), (b) precipitation (removing the effects of NDVI and temperature), (c) temperature (removing the effects of NDVI and precipitation), (e) LAI (removing the effects of precipitation and temperature), (f) precipitation (removing the effects of LAI and temperature), and (g) temperature (removing the effects of LAI and precipitation). Blank areas indicate partial correlations that failed the significance test (P > 0.05). The distribution and proportions of the area occupied by the controlling factors: (d) NDVI, precipitation and temperature; and (h) LAI, precipitation and temperature. Blank areas indicate NDVI < 0.1 or LAI ≤ 0 in Central Asia during the growing seasons.

Figure 5. The time (lag-accumulation) effects of soil moisture in combination with different factors: effects of soil moisture in combination with different factors: (a) NDVI, (b) LAI, (c) precipitation (with NDVI as the vegetation index), (d) precipitation (with LAI as the vegetation index), (e) temperature (with NDVI as the vegetation index), and (f) temperature (with LAI as the vegetation index).

Jiang, H., H. Shen, X. Li, C. Zeng, H. Liu, and F. Lei. 2019. “Extending the SMAP 9-Km Soil Moisture Product Using a Spatio-Temporal Fusion Model.” Remote Sensing of Environment 231:111224. https://doi.org/10.1016/j.rse.2019.111224.

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Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.