Interplay between land-use dynamics and changes in hydrological regime in the Vietnamese Mekong Delta

Abstract

12Policies supporting rice production and investments in water infrastructure enabled 13 intensification and diversification of farming systems in the Vietnamese Mekong Delta (VMD) 14 over the past 20 years. Yet, demands of food security, economic development, and climate 15 change continue to pose diverging and often conflicting challenges for water resources 16 management in the upper, central, and coastal zones of the delta. The major changes effected in 17 the VMD's hydrological regime and land-use patterns are acknowledged in the literature, but few 18 studies have examined the interplay between these dynamics at the delta scale. Based on time-19series maps and statistical data on land-use, flooding, and salinity intrusion, we investigated the 20 interrelations between land-use dynamics and changes in hydrological regime across the VMD in 21 three representative periods. Land-use was found to be highly variable, changing by 14.94% 22 annually between 2001 and 2012. Rice cropping underwent the greatest change, evolving from 23 single cropping of traditional varieties towards double and triple cropping of high-yielding 24 varieties. Aquaculture remained stable after rapid expansion in the 1990s and early 2000s. 25 2Meanwhile, flooding and salinity intrusion were increasingly controlled by hydrological 26 infrastructure erected to supply freshwater for agriculture. Effects of this infrastructure became 27 particularly evident from 2001 to 2012. During this period, spatial and temporal impacts on 28 flooding and salinity intrusion were found, which extended beyond the rice fields to affect 29 adjacent lands and livelihood activities. Unforeseen effects will likely be aggravated by climate 30 change, suggesting a need to rethink the scale of planning towards a more integrated hydrologic 31 approach. 32 Keywords: land-use change, hydrological regime, land-use planning, water resources 33 management, Mekong Delta, Vietnam 34 1. Introduction 35Surface water, including reservoir water and stream flows, is essential for human activities, 36 particularly for agriculture, forestry, and fisheries. Indeed, land-use and water resources are 37 reciprocally related and mutually dependent. Water availability shapes land-use patterns; and the 38 way that land is utilized affects water supplies and quality. As discussed by Calder (2005), 39 afforestation, intensive agriculture, and urbanization have changed hydrological regime, leading 40 to diminished water quality in developing countries. This has contributed to changes in the 41 global hydrological cycle, which in turn are considered a main factor causing erosion and more 42 than half of the world's soil degradation -resulting in reduced agricultural land availability. 43Understanding how changes in land-use interrelate with changes in hydrological regime is 44 therefore crucial, at the global and at the regional level. 45The interplay between land-use patterns and water resources is particularly manifest in large 46 deltas where agriculture is the dominant livelihood....

From free to forced adaptation: A political ecology of the ‘state‐society‐flood’ nexus in the Vietnamese Mekong Delta

“…Strauss () claims that the loss of traditions could be seen as a threat to the culture itself. This study suggests that the erosion of ‘riverine’ culture in the delta could be largely attributed to the land use change (Le et al ., ) and the extensive construction of flood control schemes in support of intensive agricultural production over the last two decades (Yasuyuki, ; Tran and James, ).…”

Towards risk-based flood management in highly productive paddy rice cultivation – concept development and application to the Mekong Delta

“…A small share of the overestimation of the 2011 flood might stem from the land-use data. Considering the rapid expansion of the triple season rice areas in the delta (Le et al (2018), the used land-use product of 2014 is expected to overestimate damage areas of rice paddies. Also, land-use data have a resolution of 25 250x250 m, therefore the majority of inland canals (width 10-30 m) were likely classified as rice pixels (see Fig.…”

“…Applying these damage functions to the current situation is, however, not recommended due to the massive changes in land-use and cropping system over the last two decades. For example, Le et al (2018) calculated an annual rate of change in land-use in the VMD of 14.9%…”

Towards risk-based flood management in highly productive paddy rice cultivation – concept development and application to the Mekong Delta

“…On the other hand, extreme floods can result in extensive damages as recorded during the floods in 2011 and 2000. For example, the 2000 flood, considered as a 20-year flood (Le et al, 2007), resulted in over 450 fatalities and economic losses of USD 250 million (MRC, 2012). Recent studies suggest that the frequency of such extreme events is likely to increase (Delgado et al, 2010;Hirabayashi et al, 2013).…”

“…hydropower dams), local flood control (e.g. dyke systems), climate change impacts, and sea level rise by hydrodynamic modelling (Le et al, 2007;Van, 2009;Dinh et al, 2012;Van et al, 2012;Toan, 2014;Triet et al, 2017;Dang et al, 2018). A comprehensive flood hazard analysis for the whole MD can only be found in the study of Dung et al (2015).…”