Regime shift of a large river as a response to Holocene climate change depends on land use – a numerical case study from the Chinese Loess Plateau
Abstract. The Wei River catchment in the southern part of the Chinese Loess Plateau (CLP), is one of the centers of the agricultural revolution in China. The area has experienced intense land use changes since ~6000 BCE, which makes it an ideal place to study the response of fluvial systems to anthropogenic land cover change (ALCC). We applied a numerical landscape evolution model that combines the Landlab landscape evolution model with an evapotranspiration model to investigate the direct and indirect effects of ALCC on hydrological and morphological processes in the Wei River catchment since the mid-Holocene. The results show that ALCC not only leads to changes in discharge and sediment load in the catchment but also affects their sensitivity to climate change. When the proportion of agricultural land area exceeded 50 % (around 1000 BCE), the sensitivities of discharge and sediment yield to climate change increased abruptly indicating a regime change in the fluvial catchment. It is associated with a large sediment pulse in the lower reaches. The model simulation results also show a link between human settlement, ALCC and floodplain development: Changes in agricultural land use changes lead to downstream sediment accumulation and floodplain development, which in turn leads to further spatial expansion of agriculture and human settlement.
Hao Chen et al.
Status: open (until 20 Jun 2023)
- RC1: 'Comment on egusphere-2023-62', Anonymous Referee #1, 31 May 2023 reply
- RC2: 'Comment on egusphere-2023-62', Weiming liu, 01 Jun 2023 reply
Hao Chen et al.
Hao Chen et al.
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The authors want to use the Landlab landscape evolution model coupling an evapotranspiration model to investigate the direct and indirect effects of anthropogenic land cover change on hydrological and morphological processes in the Wei River catchment since the mid-Holocene. However, two model scenarios (a model with land use and climate change, Normal, and a model without climate change, WCC) used in the Holocene simulations were equipped to show the impacts of climate change rather than land use change, the importance of which is though shown in Discussion. The scientific question mentioned in Introduction does not been directly answer. Lack of necessary information of the methods and data makes readers difficult to understand fully only by their paper. Many uncertainties originated in paleoclimate data, model parameters, model resolution, and initial topography in 6000 BCE make the results less convincible. Thus, I do not recommend the publication of current version in the journal of ESD.
1. The numerical modeling is the core method. However, it is not introduced enough in Introduction. Applications of landscape evolution modeling for other similar studies should be mentioned.
2. Line 85: what is “KK10 scenarios” in this sentence? We do not know anything about KK10 before the line. You should briefly describe what is KK10.
3. Line 99: the study area is not an East Asian monsoon region but just belongs to it.
4. Line 157: what is the time scale? daily, monthly, or yearly? what is the time range of observed data?
5. Line 183-198: a technology roadmap of model development should be given here.
6. Line 189: please describe what the tuning method looks like.
7. Line 225: in the Fig S1, sample numbers for validation may be too small, which means the high R2 cannot pass the significance test. It may bring more uncertainties into the following results.
8. Line 226-229: “the reconstructions of Holocene climate including precipitation and temperature (Peterse et al., 2011; Chen et al., 2015) are used to predict the climatic inputs, by methods of Chen et al. (2001).” makes me confused. Did you use Holocene precipitation and temperature to predict climatic inputs? What do climatic inputs mean here? What is the method of Chen et al. (2001)? In addition, the word “predicted” is inappropriate, it may be some words like “simulated” because it is nothing about the future.
9. Line 238: how about the uncertainty of KK10 database calculated from a global ALCC model for the local catchment in this study?
10. Line255-260: how did authors guarantee the reasonability of initial topography? If not, the study may be inauthentic and become a sensitivity test.
11. Line 270: what is the method proposed by Chang et al.(2016)?
12. Line 272-273: please show the acknowledged evaluation criterion and its results in a figure for the mentioned accepted calibration results.
13. Line 315: what are the climatic inputs for Normal and WCC scenarios, respectively? What is the temporal and spatial resolution of model outputs?
14. Line 345: why constant for each 500 years?
15. Line 354: what is the relation between runoff and discharge? how did authors calculate the discharge by runoff?
16. From the difference of model results for the two scenarios, impacts of climate change can be identified but no evidence shows the effects of ALCC.
17. In section 5.1, the sensitivity of discharge and sediment yield to the climate changes is based on statistical analysis rather than the ALCC impact on land-air interaction. It belongs to a complex climate system, so the title “Regime shift of a large river as a response to Holocene climate change depends on land use” is difficult to be addressed mechanically without climate-landscape evolution coupled modeling.