Hydrological impacts of reforesting degraded pasture land in the Middle Mountain Zone of Central Nepal Chandra Prasad Ghimire VRIJE UNIVERSITEIT Hydrological impacts of reforesting degraded pasture land in the Middle Mountain Zone of Central Nepal ACADEMISCH PROEFSCHRIFT ter verkrijging van de graad Doctor aan de Vrije Universiteit Amsterdam, op gezag van de rector magnificus prof.dr. F.A. van der Duyn Schouten, in het openbaar te verdedigen ten overstaan van de promotiecommissie van de Faculteit der Aard- en Levenswetenschappen op dinsdag 3 juni 2014 om 11.45 uur in de aula van de universiteit, De Boelelaan 1105 door Chandra Prasad Ghimire geboren te Chitwan, Nepal promotor: prof.dr. L.A. Bruijnzeel copromotoren: dr.ir. M.W. Lubczynski prof.dr. M. Bonell reading committee: prof.dr. M.F.P. Bierkens prof.dr. J. Čermák prof.dr. D. Hölscher dr. H.J. van Meerveld dr. C. van der Tol paranymphs: Mireia Romaguera Yijian Zeng ITC dissertation number 248 ITC, P.O. Box 217, 7500 AE Enschede, The Netherlands ISBN 978-90-365-3684-4 DOI http://dx.doi.org/10.3990/19789036536844 Cover designed by Chandra Prasad Ghimire Printed by ITC Printing Department Copyright © 2014 by Chandra Prasad Ghimire Dedicated to those who made this study possible and also to those who opened my eyes “All search for happiness is misery and leads to more misery.” - Shri Nisargadattta Maharaj Table of Contents Chapter 1 General introduction .......................................................................... 1 1.1 Forest and water ................................................................................ 1 1.2 Land degradation, reforestation and dry season flows in theLesser Himalaya of Nepal ............................................................................. 5 1.3 Research objectives ........................................................................... 6 1.4 Outline of the thesis ........................................................................... 8 References: .................................................................................................. 9 Chapter 2 Rainfall interception by natural and planted forests in the Middle Mountains of Central Nepal .............................................................................. 17 2.1 Introduction ..................................................................................... 18 2.2 Study area ........................................................................................ 19 2.3 Methods ........................................................................................... 22 2.3.1 Rainfall .................................................................................. 22 2.3.2 Throughfall .................................................................................. 23 2.3.3 Stemflow ..................................................................................... 23 2.3.4 Additional meteorological measurements ................................... 24 2.3.5 Modelling rainfall interception .................................................... 24 2.3.6 Derivation of canopy parameters ........................................... 26 2.3.7 Wet-canopy evaporation ........................................................ 26 2.4 Results ............................................................................................. 27 2.4.1 Rainfall characteristics ................................................................ 27 2.4.2 Throughfall, stemflow and derived interception loss ............ 28 2.4.3 Canopy parameters ................................................................ 30 2.4.4 Interception model application .............................................. 30 2.5 Discussion ....................................................................................... 34 2.5.1 Rainfall characteristics ................................................................ 34 2.5.2 Canopy parameters ................................................................ 37 2.5.3 Wet-canopy evaporation .............................................................. 38 2.5.4 Rainfall interception .............................................................. 39 2.6 Conclusion ....................................................................................... 41 References: ................................................................................................ 42 Chapter 3 Transpiration, canopy conductance and decoupling coefficient of two contrasting forest types in the Lesser Himalaya of Central Nepal ............. 49 3.1 Introduction ..................................................................................... 50 3.2 Study area ........................................................................................ 52 3.3 Methods ........................................................................................... 56 3.3.1 Environmental monitoring ..................................................... 56 3.3.2 Sap flow measurements ......................................................... 56 3.3.3 Modeling sap flow for gap filling .......................................... 61 3.3.4 Tree transpiration at stand level ............................................ 62 3.3.5 Canopy conductance and decoupling coefficient .................. 62 3.3.6 Total evapotranspiration ........................................................ 63 3.4 Results ............................................................................................. 65 3.4.1 Meteorological measurements ............................................... 65 3.4.2 Soil moisture ............................................................................... 66 3.4.3 Sapwood area .............................................................................. 66 3.4.4 Diurnal and radial variations in sap flux density ................... 68 3.4.5 Daily, seasonal and annual stand transpiration ...................... 71 3.4.6 Canopy conductance and decoupling coefficient .................. 73 3.5 Discussion ....................................................................................... 74 3.5.1 Control of transpiration ............................................................... 74 3.5.2 Canopy conductance and decoupling coefficient .................. 80 3.5.3 Evapotranspiration and implication for dry season flows ..... 83 3.6 Conclusion ....................................................................................... 86 References: ................................................................................................ 87 Chapter 4 Reforesting severely degraded grassland in the Lesser Himalaya of Nepal: Effects on soil hydraulic conductivity and overland flow production ... 99 4.1 Introduction ................................................................................... 100 4.2 Study area ...................................................................................... 103 4.3 Methods ......................................................................................... 106 4.3.1 Field measurements of soil hydraulic conductivity ............. 106 4.3.2 Experimental design ............................................................ 108 4.3.3 Rainfall intensity ................................................................. 111 4.3.4 Overland flow ...................................................................... 111 4.3.5 Additional soil physical and chemical properties ................ 112 4.3.6 Data analysis ........................................................................ 112 4.3.6.1 Inferring the hydrological consequences of different levels of anthropogenic pressure ...................................... 112 4.3.6.2 Statistical analysis ............................................................ 113 4.3.6.3 Spatial analysis ................................................................. 114 4.4 Results ........................................................................................... 115 4.4.1 Soil physical and chemical properties ................................. 115 4.4.2 Exploratory analysis of field-saturated soil hydraulic conductivity ......................................................................... 117 4.4.3 Spatial structure ................................................................... 118 4.4.4 Rainfall intensity, overland flow, and hydrological consequences of anthropogenic pressure............................................ 120 4.5 Discussion ..................................................................................... 123 4.5.1 Impacts of land use/land cover on spatial correlation length and soil hydraulic conductivity................................. 123 4.5.2 Kfs, overland flow generation and forest management ........ 127 4.5.3 Implications for dry season flows ........................................ 130 4.5.4 Footpaths as source areas of storm runoff ........................... 131 4.5.5 On the need to protect the remaining natural forests of the Middle Mountains.......................................................... 132 4.6 Conclusions ................................................................................... 133 References: .............................................................................................. 135 Chapter 5 The effects of sustained forest use on hillslope soil hydraulic conductivity in the Middle Mountains of Central Nepal ................................. 147 5.1 Introduction ..................................................................................