Abstract
Terrestrial vegetation growth activity plays pivotal roles on regional development, which has attracted wide attention especially in water resources shortage areas. The paper investigated the spatiotemporal change characteristics of vegetation growth activity using satellite-based Vegetation Health Indices (VHIs) including smoothed Normalized Difference Vegetation Index (SMN), smoothed Brightness Temperature (SMT), Vegetation Condition Index (VCI), Temperature Condition Index (TCI) and VHI, based on 7-day composite temporal resolution and 16 km spatial resolution gridded data, and also estimated the drought conditions for the period of 1982–2016 in Jing-Jin-Ji region of China. The Niño 3.4 was used as a substitution of El Niño Southern Oscillation (ENSO) to reveal vegetation sensitivity to ENSO using correlation and wavelet analysis. Results indicated that monthly SMN has increased throughout the year especially during growing season, starts at approximate April and ends at about October. The correlation analysis between SMN and SMT, SMN and precipitation indicated that the vegetation growth was affected by joint effects of temperature and precipitation. The VCI during growing season was positive trends dominated and vice versa for TCI. The relationships between VHIs and drought make it possible to identify and quantify drought intensity, duration and affected area using different ranges of VHIs. Generally, the intensity and affected area of drought had mainly decreased, but the trends varied for different drought intensities, regions and time periods. Large-scale global climate anomalies such as Niño 3.4 exerted obvious impacts on the VHIs. The Niño 3.4 was mainly negatively correlated to VCI and positively correlated to TCI, and the spatial distributions of areas with positive (negative) correlation coefficients were mainly opposite. The linear relationships between Niño 3.4 and VHIs were in accordance with results of nonlinear relationships revealed using wavelet analysis. The results are of great importance to assess the vegetation growth activity, to monitor and quantify drought using satellite-based VHIs in Jing-Jin-Ji region.
Highlights
The Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC) showed that the global average surface air temperature had increased by 0.85 ± 0.21 °C from 1880 to 2012
The results showed that about 77% of the Jing-Jin-Ji region had positive slopes for Vegetation Condition Index (VCI) (Fig. 3b), 38% based on the Temperature Condition Index (TCI) (Fig. 3d) and 65% for Vegetation Health Indices (VHIs) (Fig. 3f), indicating that the vegetation growth had enhanced in majority of Jing-Jin-Ji region for both VCI and VHI
Using satellite-based VHIs, the paper assessed the spatiotemporal variability of vegetation growth activity for both regional average and individual grids, and estimated the change characteristics of drought for the period of 1982–2016 in the Jing-Jin-Ji region
Summary
The Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC) showed that the global average surface air temperature had increased by 0.85 ± 0.21 °C from 1880 to 2012. It is difficult to determine the onset, end and severity of the d rought[13,14] Various drought indices such as Palmer Drought Severity Index (PDSI), Crop Moisture Index (CMI), Drought Area Index (DAI), Normalized Soil Water Index (NSWI), Reconnaissance Drought Index (RDI), self-calibrating PDSI (sc_PDSI), Soil Moisture Anomaly Percentage Index (SMAPI), Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI) have been proposed to monitor, quantify and analyze the drought events and their characteristics mainly from three aspects including intensity, duration and spatial coverage[15,16,17].
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