By means of GPS measurement data in research areas and combined with GIS spatial analysis and statistical regression method

this paper validated the foreign critical relations for occurring ephemeral and gully erosion in the hilly-gully region of Loess Plateau and established the critical relations for determining ephemeral gully erosion and gully erosion areas

respectively.The research results indicated that in the Loess Plateau area

with an increase of slope gradient

the threshold values(a) for occurring ephemeral gully and gully erosion increased;and meanwhile

the high rainfall intensity caused the exponential value(b) of the critical upslope area decreased

which reduced the effect of the critical upslope area.Under the same condition

occurring ephemeral gully erosion needed less critical upslope area than that of occurring gully erosion;and with the same critical upslope area

the occurrence of gully erosion needed higher slope gradient than that of occurring ephemeral gully erosion.By using the foreign critical relations of ephemeral gully and gully erosion to draw occurring areas of ephemeral gully and gully area in loess hilly-gully region

the predicted ephemeral and gully erosion area was over-estimated.By using our establishing critical relations of ephemeral gully and gully to delineate occurring areas of ephemeral gully and gully area in the loess hilly-gully region

the predicted ephemeral and gully erosion area very matched to the actual distribution of ephemeral and gully erosion in the field.That is

ephemeral gully erosion mainly happened on hillslopes with 15°~35°

accounted for 60% of the hillslope area;and the gully erosion mainly occurred on gully slopes with more than 35°

occupied 93% of the whole gully slope area.