Research on the future change trend of global runoff into the sea based on SSA-BP neural network model

doi:10.12006/j.issn.1673-1719.2023.243

Abstract

Abstract:

Runoff into the sea is an important link in the water cycle. Exploring the spatial and temporal variation characteristics of global runoff into the sea under the background of climate change can provide a basis for the rational utilization of water resources. Based on the monthly discharge of 376 outflow rivers around the world, ERA5-LAND reanalysis data and 10 global climate models, a precipitation-runoff relationship model based on the SSA-BP neural network was constructed to analyze the spatiotemporal change characteristics of the global runoff into the sea during the historical period (1961-2020) and the future (2021-2100) under three scenarios (SSP1-2.6, SSP3-7.0 and SSP5-8.5). The results are as follows. (1) On a global scale, from 1961 to 2020, the multi-year average annual runoff into the sea was 37423 km³. From 2021 to 2100, the global annual runoff into the sea will show an increasing trend under the three future scenarios, with a significant trend under the SSP1-2.6 scenario. Compared with the base period, the late 21st century showed the largest increase. (2) On an intercontinental scale, during historical periods, Africa’s runoff into the sea showed a significant decreasing trend, while North America showed a significant increasing trend. From 2021 to 2100, Asia and North America will show an increasing trend under three scenarios, Oceania will show a decreasing trend, and there are obvious differences among the scenarios for the remaining continents. (3) In terms of latitudinal distribution, the change trend in the low latitudes of the Northern and Southern Hemispheres during the historical period was not significant; the mid-latitude Northern Hemisphere showed a weak decreasing trend, the Southern Hemisphere showed a significant decreasing trend; and the high latitudes of the Northern Hemisphere showed a significant increasing trend. From 2021 to 2100, from low to high emission scenarios, the increasing trend of runoff into the sea in the low latitudes of the Northern Hemisphere and the decreasing trend in the Southern Hemisphere become more and more significant; in the mid-to-high latitudes of the Northern Hemisphere, the significant increase in the low emission scenario changes to the significant decrease in the medium and high emission scenario; The mid-latitudes of the Southern Hemisphere show a significant increasing trend under the low emission scenario, but the trend is not significant under the medium and high emission scenario.

Key words: Runoff into the sea, Trend estimation, SSA-BP model, Global scale

ZHAO Peng, JIANG Tong, SU Bu-Da, GAO Miao-Ni. Research on the future change trend of global runoff into the sea based on SSA-BP neural network model[J]. Climate Change Research, 2024, 20(2): 182-192.

Figures/Tables 9

Fig. 1 Controlled hydrological stations

Fig. 2 BP neural network structure (a) and SSA-BP neural network model calculation process (b)

Table 1 SSA-BP neural network model simulation and verification

Fig. 3 Inter-annual (a), inter-decadal (b), monthly (c) and seasonal (d) changes in global runoff into the sea from 1961 to 2020

Fig. 4 Changes of annual (a) and monthly (b) global runoff into the sea from 2021 to 2100. (The solid line represents the multi-model ensemble, and the shaded represents the upper and lower bounds of the multiple models)

Fig. 5 The changes in major global outflow rivers during historical period and under different scenarios in the future

Fig. 6 The changes of monthly runoff into the sea from all continents around the world from 1961 to 2020

Table 2 Inter-annual changes in runoff into the sea from all continents in the world under different scenarios from 2021 to 2100 km3/(10 a)

Table 3 Inter-annual changes in runoff into the sea at various latitudes around the world under different scenarios from 2021 to 2100 km3/(10 a)

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