@article{fdi:010070997,
  title = {{T}he paradoxical evolution of runoff in the pastoral {S}ahel : analysis of the hydrological changes over the {A}goufou watershed ({M}ali) using the {KINEROS}-2 model},
  author = {{G}al, {L}a{\¨e}titia and {G}rippa, {M}. and {H}iernaux, {P}. and {P}ons, {L}. and {K}ergoat, {L}.},
  editor = {},
  language = {{ENG}},
  abstract = {{I}n recent decades, the {S}ahel has witnessed a paradoxical increase in surface water despite a general precipitation decline. {T}his phenomenon, commonly referred to as "the {S}ahelian paradox", is not completely understood yet. {T}he role of cropland expansion due to the increasing food demand by a growing population has been often put forward to explain this situation for the cultivated {S}ahel. {H}owever, this hypothesis does not hold in pastoral areas where the same phenomenon is observed. {S}everal other processes, such as the degradation of natural vegetation following the major droughts of the 1970s and the 1980s, the development of crusted topsoils, the intensification of the rainfall regime and the development of the drainage network, have been suggested to account for this situation. {I}n this paper, a modeling approach is proposed to explore, quantify and rank different processes that could be at play in pastoral {S}ahel. {T}he kinematic runoff and erosion model ({KINEROS}-2) is applied to the {A}goufou watershed (245 km(2)), in the {G}ourma region in {M}ali, which underwent a significant increase of surface runoff during the last 60 years. {T}wo periods are simulated, the "past" case (1960-1975) preceding the {S}ahelian drought and the "present" case (2000-2015). {S}urface hydrology and land cover characteristics for these two periods are derived by the analysis of aerial photographs, available in 1956, and high-resolution remote sensing images in 2011. {T}he major changes identified are (1) a partial crusting of isolated dunes, (2) an increase of drainage network density, (3) a marked decrease in vegetation with the nonrecovery of tiger bush and vegetation growing on shallow sandy soils, and (4) important changes in soil properties with the apparition of impervious soils instead of shallow sandy soil. {T}he {KINEROS}-2 model was parameterized to simulate these changes in combination or independently. {T}he results obtained by this model display a significant increase in annual discharge between the "past" and the "present" case (p value < 0.001), which is consistent with observations, despite a slight overestimation of the past discharge. {M}ean annual discharges are estimated at 0.51 x 10(6) m(3) (2.1 mm yr(-1)) and 3.29 x 10(6) m(3) (13.4 mm yr(-1)) for past and present, respectively. {C}hanges in soil properties and vegetation cover (tiger bush thickets and grassland on shallow sandy soil) are found to be the main factors causing this increase of simulated runoff, with the drainage network development contributing to a lesser extent but with a positive feedback. {T}hese results shed a new light on the {S}ahelian paradox phenomenon in the absence of land use change and call for further tests in other areas and/or with other models. {T}he synergetic processes highlighted here could play a role in other {S}ahelian watersheds where runoff increase has been also observed.},
  keywords = {{MALI} ; {SAHEL}},
  booktitle = {},
  journal = {{H}ydrology and {E}arth {S}ystem {S}ciences},
  volume = {21},
  numero = {9},
  pages = {4591--4613},
  ISSN = {1027-5606},
  year = {2017},
  DOI = {10.5194/hess-21-4591-2017},
  URL = {https://www.documentation.ird.fr/hor/fdi:010070997},
}