黃(huang)(huang)土高(gao)(gao)(gao)(gao)原(yuan)(yuan)地勢西北高(gao)(gao)(gao)(gao),東(dong)南(nan)低(di),自西北向東(dong)南(nan)呈波狀下降。以(yi)六(liu)盤(pan)山和呂梁山為(wei)(wei)界把黃(huang)(huang)土高(gao)(gao)(gao)(gao)原(yuan)(yuan)分為(wei)(wei)東(dong)、中、西三部(bu)分:六(liu)盤(pan)山以(yi)西的黃(huang)(huang)土高(gao)(gao)(gao)(gao)原(yuan)(yuan)西部(bu),海拔2000-3000米(mi),是黃(huang)(huang)土高(gao)(gao)(gao)(gao)原(yuan)(yuan)地勢高(gao)(gao)(gao)(gao)的地區。
六盤(pan)山與呂梁山之(zhi)司(si)的黃土高(gao)原中部(bu),海拔(ba)1000-2000米,是黃土高(gao)原的主體。呂梁山以東的黃土高(gao)原東部(bu),地勢(shi)降(jiang)至500-1000米,河谷(gu)平原占(zhan)有較大比例。
據(ju)此可(ke)將黃土高原(yuan)分為山(shan)地(di)區(qu)、黃土丘陵區(qu)、黃土塬區(qu)、黃土臺塬區(qu)、河谷平(ping)原(yuan)區(qu)。
黃土高原(yuan)基巖(yan)構(gou)造(zao)以(yi)六(liu)盤山為(wei)界分為(wei)東(dong)西(xi)(xi)兩部(bu)分,西(xi)(xi)部(bu)屬西(xi)(xi)域陸(lu)(lu)塊,東(dong)部(bu)屬華北陸(lu)(lu)塊。六(liu)盤山以(yi)西(xi)(xi)黃土高原(yuan)以(yi)新(xin)生代斷陷(xian)盆地(di)(di)為(wei)構(gou)造(zao)特征,隴中(zhong)盆地(di)(di)黃土下伏(fu)基巖(yan)為(wei)直接(jie)堆(dui)積在(zai)(zai)古老巖(yan)層(ceng)之(zhi)上的(de)(de)中(zhong)新(xin)世到上新(xin)世早期的(de)(de)甘肅(su)群。甘肅(su)群堆(dui)積后,上新(xin)世晚(wan)期地(di)(di)面抬升,黃河(he)及其(qi)支流挑河(he)、祖歷(li)河(he)、葫蘆河(he)隨抬升而下切,基巖(yan)地(di)(di)面成(cheng)為(wei)起伏(fu)較(jiao)大(da)的(de)(de)丘陵(ling)狀。甘肅(su)群為(wei)一套(tao)含有(you)石膏的(de)(de)紫紅色(se)粘土,砂(sha)質(zhi)粘土,砂(sha)巖(yan)和(he)砂(sha)礫巖(yan)。其(qi)成(cheng)巖(yan)性差(cha),抗蝕(shi)力(li)較(jiao)弱,在(zai)(zai)地(di)(di)下水浸泡和(he)潤滑作(zuo)用下極易發生重力(li)侵蝕(shi),常形成(cheng)大(da)型滑坡(po)。六(liu)盤山以(yi)東(dong)的(de)(de)華北陸(lu)(lu)臺(tai)(tai)由鄂爾多(duo)斯(si)臺(tai)(tai)向斜和(he)山西(xi)(xi)臺(tai)(tai)背(bei)斜構(gou)成(cheng),中(zhong)間夾(jia)以(yi)黃河(he)凹陷(xian)。鄂爾多(duo)斯(si)臺(tai)(tai)向斜和(he)山西(xi)(xi)臺(tai)(tai)背(bei)斜是未經褶皺變(bian)動(dong)的(de)(de)前震旦紀陸(lu)(lu)臺(tai)(tai)。
陜(shan)北(bei)、隴東(dong)(dong)和晉西的(de)鄂(e)爾(er)多(duo)斯臺(tai)向斜(xie)(xie)在(zai)中生(sheng)代(dai)發展(zhan)成(cheng)為(wei)(wei)一個(ge)大型的(de)內陸盆地(di),當(dang)時地(di)勢東(dong)(dong)南高(gao)(gao)西北(bei)低,與今況剛好相反。西北(bei)部堆積了厚(hou)達1500米(mi)完整的(de)中生(sheng)代(dai)地(di)層序列。其中神木,準(zhun)格爾(er)旗一帶廣(guang)泛(fan)出露的(de)中生(sheng)代(dai)灰(hui)綠色、黃(huang)綠色長石砂巖,當(dang)地(di)叫(jiao)砒(pi)砂巖,極易風化侵蝕,是(shi)(shi)當(dang)地(di)及黃(huang)河(he)中粗砂的(de)主(zhu)要(yao)來源。燕山(shan)(shan)(shan)運動(dong)使鄂(e)爾(er)多(duo)斯臺(tai)向斜(xie)(xie)抬升,邊(bian)緣發生(sheng)斷陷,形成(cheng)汾(fen)渭(wei)谷地(di)等一系列地(di)塹谷地(di),到(dao)第(di)三紀的(de)中新(xin)世末(mo)鄂(e)爾(er)多(duo)斯臺(tai)向斜(xie)(xie)成(cheng)為(wei)(wei)準(zhun)平原(yuan)(yuan)。上新(xin)世鄂(e)爾(er)多(duo)斯高(gao)(gao)原(yuan)(yuan)長城(cheng)以南的(de)準(zhun)平原(yuan)(yuan)面(mian)上廣(guang)泛(fan)堆積了三趾(zhi)(zhi)馬紅土(tu),從三趾(zhi)(zhi)馬紅土(tu)的(de)分布(bu)和厚(hou)度(du)看,上新(xin)世時長城(cheng)以南,渭(wei)北(bei)北(bei)山(shan)(shan)(shan)以北(bei),六盤山(shan)(shan)(shan)與呂梁山(shan)(shan)(shan)之間(jian)是(shi)(shi)一個(ge)淺凹形的(de)巨大盆地(di)。地(di)勢西北(bei)高(gao)(gao),東(dong)(dong)南低,己與今相同。三趾(zhi)(zhi)馬紅土(tu)透水性(xing)極差,是(shi)(shi)黃(huang)土(tu)下覆的(de)主(zhu)要(yao)不透水層,而且三趾(zhi)(zhi)馬紅土(tu)容易吸水膨脹,是(shi)(shi)黃(huang)土(tu)高(gao)(gao)原(yuan)(yuan)大型滑坡的(de)主(zhu)要(yao)滑移層。上新(xin)世晚期到(dao)更新(xin)世,鄂(e)爾(er)多(duo)斯高(gao)(gao)原(yuan)(yuan)邊(bian)緣如汾(fen)渭(wei)地(di)塹谷地(di)進一步發展(zhan),同時高(gao)(gao)原(yuan)(yuan)整體(ti)發生(sheng)掀斜(xie)(xie)運動(dong),使地(di)面(mian)形成(cheng)自西北(bei)向東(dong)(dong)南傾斜(xie)(xie)的(de)斜(xie)(xie)面(mian),控制著河(he)流的(de)流向。在(zai)地(di)貌演變過(guo)程中溝谷的(de)發展(zhan),谷間(jian)地(di)有些形成(cheng)面(mian)積不大的(de)平臺(tai),有些成(cheng)為(wei)(wei)長條狀(zhuang)或橢圓狀(zhuang)丘(qiu)陵,它們是(shi)(shi)鄂(e)爾(er)多(duo)斯高(gao)(gao)原(yuan)(yuan)塬、梁、峁(mao)地(di)形的(de)基礎。
山(shan)西(xi)臺(tai)背(bei)斜(xie)包括太(tai)行山(shan)以(yi)西(xi)、呂梁(liang)山(shan)以(yi)東(dong)。五(wu)臺(tai)山(shan)是山(shan)西(xi)臺(tai)背(bei)斜(xie)古(gu)老的(de)部(bu)分,并以(yi)此為頂(ding)點向(xiang)南沿伸,東(dong)部(bu)為太(tai)行山(shan),西(xi)部(bu)為呂梁(liang)山(shan),兩山(shan)之間為凹陷部(bu)分。古(gu)生(sheng)代以(yi)來,凹陷部(bu)分堆(dui)積(ji)了巨(ju)厚(hou)的(de)陸相碎屑(xie)物。燕山(shan)運(yun)動后(hou)山(shan)西(xi)臺(tai)背(bei)斜(xie)中(zhong)部(bu)受斷(duan)裂作(zuo)用(yong)晉(jin)中(zhong)大(da)斷(duan)谷(gu)開始形(xing)成(cheng)。中(zhong)新(xin)世(shi)末(mo)晉(jin)中(zhong)南的(de)漳(zhang)沁地(di)區形(xing)成(cheng)準(zhun)平原,其后(hou)接受了上(shang)新(xin)世(shi)的(de)三趾馬(ma)紅土堆(dui)積(ji)。喜馬(ma)拉(la)雅運(yun)動使山(shan)西(xi)臺(tai)背(bei)斜(xie)進一(yi)步上(shang)升,晉(jin)中(zhong)斷(duan)谷(gu)不斷(duan)發育,河流下(xia)切,到更新(xin)世(shi)黃土堆(dui)積(ji)時地(di)面形(xing)成(cheng)起伏(fu)較大(da)的(de)丘陵、成(cheng)為山(shan)地(di)與斷(duan)谷(gu)、盆(pen)地(di)相間分布的(de)地(di)形(xing)特(te)征(zheng)。
●黃土地層與黃土分布
黃土高原原生黃土是第四紀冰期干冷氣候條件下的風塵堆積物,次生黃土是原生黃土經洪積、沖積改造而成的。在第四紀黃土堆積時期,隨著冰期、間冰期的氣候旋迥,黃土地層呈現黃土與古土壤的更替變化。根據黃土中的古土壤,黃土地層自下而上可以分為午城黃土、離石黃上、馬蘭黃土和世黃土。按洛川黑木溝黃土剖面,第十五層黃土下界面之下為早更新世午城黃土。古土(tu)(tu)(tu)(tu)(tu)壤上界面之下至(zhi)第十五層(ceng)黃(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)下界面之間為(wei)(wei)(wei)(wei)中更(geng)新(xin)離石(shi)黃(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)。黃(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)層(ceng)是(shi)形(xing)(xing)成(cheng)于晚更(geng)新(xin)世(shi)的(de)馬(ma)蘭黃(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)。馬(ma)蘭黃(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)之上的(de)黑滬土(tu)(tu)(tu)(tu)(tu)為(wei)(wei)(wei)(wei)形(xing)(xing)成(cheng)于古土(tu)(tu)(tu)(tu)(tu)壤層(ceng)。黃(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)高(gao)原(yuan)黃(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)地(di)(di)層(ceng)的(de)分布厚(hou)(hou)(hou)(hou)度(du)在六盤(pan)(pan)山與呂梁山之間一般為(wei)(wei)(wei)(wei)150-250米(mi)(mi),六盤(pan)(pan)山以(yi)(yi)西一般在100米(mi)(mi)以(yi)(yi)內。不同地(di)(di)層(ceng)黃(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)厚(hou)(hou)(hou)(hou)度(du)也不相同:午城黃(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)厚(hou)(hou)(hou)(hou)度(du)不大,洛(luo)川(chuan)(chuan)黑木溝為(wei)(wei)(wei)(wei)58米(mi)(mi),山西午城為(wei)(wei)(wei)(wei)17.5米(mi)(mi)。離石(shi)黃(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)是(shi)黃(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)高(gao)原(yuan)黃(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)地(di)(di)層(ceng)的(de)主體,一般厚(hou)(hou)(hou)(hou)度(du)100-150米(mi)(mi),厚(hou)(hou)(hou)(hou)度(du)分布在徑河與洛(luo)河的(de)中游地(di)(di)區。馬(ma)蘭黃(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)分布極為(wei)(wei)(wei)(wei)廣泛,一般厚(hou)(hou)(hou)(hou)度(du)10-30米(mi)(mi),天水附近小于10米(mi)(mi),董(dong)志(zhi)源9.6米(mi)(mi),洛(luo)川(chuan)(chuan)源10米(mi)(mi)左右。世(shi)黃(huang)(huang)(huang)土(tu)(tu)(tu)(tu)(tu)厚(hou)(hou)(hou)(hou)度(du)-般為(wei)(wei)(wei)(wei)2-3米(mi)(mi),其中的(de)黑滬土(tu)(tu)(tu)(tu)(tu)層(ceng)厚(hou)(hou)(hou)(hou)度(du)1-2米(mi)(mi)。
●黃土粒度與黃土性質
黃土是在風力吹揚搬運下,在干旱半干旱環境堆積的風成堆積物,經過長距離的搬運和分選,其物質組成具有高度的均一性。黃土粒度以粒徑0.05-0.005毫米的粉砂為主,所占比例58-75%。其次為粒徑>0.05毫米的細砂,占15-32%。粒徑0<0.005毫米的粘土占10%左右。黃土粒徑存在著自西北向東南逐漸變細的特點,這一特點以砂粒和粘粒的變化明顯。北部榆林附近砂粒的重量比在30%以上,向南到清澗、延安附近降為20%左右,咸陽、寶雞一帶降至10%上下。相反,榆林粘粒僅占10%左右,延安、清澗一帶增至13-18%,咸陽、寶雞為23-26%。這樣自西北向東南根據黃土粒徑可以把黃土高原黃土分為砂黃土、典型黃土和粘黃土三個帶:靜樂北-綏德-子長-環縣-海原一線以北為砂黃上帶。陽泉-沁縣-浮山北-淳化-秦安-渭源以北,砂黃土帶以南為典型黃土帶。典型黃土帶以南為粘黃土帶。黃土在南北方向上的粒度分異對黃土地貌及土壤侵蝕具有深刻的影響。
黃(huang)土含有60多(duo)種礦物,其中(zhong)(zhong)石(shi)英占(zhan)重量的50%左(zuo)右(you)(you),長石(shi)占(zhan)20%左(zuo)右(you)(you),碳(tan)酸鈣占(zhan)10%左(zuo)右(you)(you)。就化(hua)(hua)(hua)學(xue)(xue)組成而言,以(yi)二(er)(er)氧(yang)化(hua)(hua)(hua)硅占(zhan)優勢(shi)(50%),其次(ci)為三氧(yang)化(hua)(hua)(hua)二(er)(er)氯(lv)(8-15%),氧(yang)化(hua)(hua)(hua)鈣(10%左(zuo)右(you)(you)),以(yi)及三氧(yang)化(hua)(hua)(hua)二(er)(er)鐵,氧(yang)化(hua)(hua)(hua)鎂,氧(yang)化(hua)(hua)(hua)鉀(jia),氧(yang)化(hua)(hua)(hua)鈉等,黃(huang)土中(zhong)(zhong)易溶性化(hua)(hua)(hua)學(xue)(xue)成份含量較高。
黃(huang)(huang)土(tu)(tu)(tu)結構為“點、棱接觸(chu)支架式(shi)多孔(kong)結構”,土(tu)(tu)(tu)體(ti)(ti)疏(shu)松(song),垂直節理發(fa)育,極易滲水(shui)(shui)(shui)。黃(huang)(huang)土(tu)(tu)(tu)中(zhong)細粒(li)物質如粘土(tu)(tu)(tu)、易溶性鹽類、石膏、碳酸鹽等(deng)在(zai)干燥時固結成(cheng)聚積(ji)體(ti)(ti),使黃(huang)(huang)土(tu)(tu)(tu)具(ju)有(you)較強的(de)強度,而遇水(shui)(shui)(shui)后(hou)隨著礦物溶解(jie)與分散,土(tu)(tu)(tu)體(ti)(ti)會(hui)迅速分散、崩解(jie)。黃(huang)(huang)土(tu)(tu)(tu)的(de)抗侵蝕(shi)能(neng)力很弱。黃(huang)(huang)土(tu)(tu)(tu)中(zhong)孔(kong)隙(xi)度-般可達45-50%,尤(you)其大孔(kong)隙(xi)特別(bie)突出(chu),當受水(shui)(shui)(shui)浸潤后(hou)上體(ti)(ti)在(zai)自重和上部壓力作(zuo)用下,易發(fa)生(sheng)濕陷。同時大孔(kong)隙(xi)也成(cheng)為土(tu)(tu)(tu)體(ti)(ti)中(zhong)水(shui)(shui)(shui)體(ti)(ti)和細粒(li)物質遷(qian)移的(de)通道,使黃(huang)(huang)土(tu)(tu)(tu)易發(fa)生(sheng)潛蝕(shi)。
黃土(tu)(tu)高(gao)原(yuan)是新構(gou)造(zao)運動(dong)比較活躍的(de)區(qu)(qu)(qu)域,新構(gou)造(zao)運動(dong)的(de)主要表現(xian)(xian)是高(gao)原(yuan)內(nei)部(bu)間歇性的(de)大(da)(da)(da)面積整體抬(tai)(tai)(tai)升(sheng)(sheng),同時周圍的(de)拗陷區(qu)(qu)(qu)域不斷地(di)沉降。從黃土(tu)(tu)高(gao)原(yuan)廣(guang)大(da)(da)(da)地(di)區(qu)(qu)(qu)河(he)谷多發育有3-4級階地(di)等判斷,第四紀以來(lai)黃上高(gao)原(yuan)以抬(tai)(tai)(tai)升(sheng)(sheng)為(wei)主,抬(tai)(tai)(tai)升(sheng)(sheng)幅度在(zai)150-30米,地(di)殼(ke)抬(tai)(tai)(tai)升(sheng)(sheng)有利河(he)流下(xia)切(qie)和侵蝕地(di)貌發育,也有利于土(tu)(tu)壤侵蝕過程的(de)加強。黃土(tu)(tu)高(gao)原(yuan)內(nei)部(bu)六盤山(shan)是新構(gou)造(zao)運動(dong)的(de)抬(tai)(tai)(tai)升(sheng)(sheng)中心,據現(xian)(xian)代水(shui)(shui)準(zhun)測(ce)量(liang),目前(qian)的(de)抬(tai)(tai)(tai)升(sheng)(sheng)速(su)度為(wei)20毫米/年(nian)。六盤山(shan)以西地(di)區(qu)(qu)(qu)抬(tai)(tai)(tai)升(sheng)(sheng)量(liang)大(da)(da)(da)于以東地(di)區(qu)(qu)(qu),抬(tai)(tai)(tai)升(sheng)(sheng)在(zai)華家(jia)嶺一帶,據1934-1955年(nian)隴(long)海鐵(tie)路水(shui)(shui)準(zhun)測(ce)量(liang),隴(long)西、渭源等地(di)現(xian)(xian)代抬(tai)(tai)(tai)升(sheng)(sheng)速(su)度為(wei)31.4毫米/年(nian),隆德、莊浪一帶溝床下(xia)切(qie)速(su)率達45-240毫米/100年(nian)。
華(hua)家嶺以(yi)(yi)南地(di)區(qu)河(he)(he)谷(gu)狹窄,一(yi)(yi)般(ban)有(you)3-4級(ji)階地(di),華(hua)家嶺以(yi)(yi)北(bei)河(he)(he)谷(gu)較(jiao)寬闊,只有(you)2-3級(ji)階地(di)發(fa)育(yu)(yu),所(suo)以(yi)(yi)華(hua)家嶺以(yi)(yi)南抬升幅度(du)(du)更大。六(liu)盤山(shan)(shan)(shan)以(yi)(yi)東(dong)(dong)地(di)區(qu)白于山(shan)(shan)(shan)至東(dong)(dong)勝(sheng)一(yi)(yi)帶(dai)是新(xin)(xin)構(gou)(gou)造(zao)運(yun)動(dong)抬升的(de)(de)(de)中(zhong)心。保德附近現代抬升速度(du)(du)在3毫(hao)米/年(nian)左(zuo)右。山(shan)(shan)(shan)西臺背斜新(xin)(xin)構(gou)(gou)造(zao)運(yun)動(dong)抬升幅度(du)(du)較(jiao)大在五臺山(shan)(shan)(shan)-恒(heng)山(shan)(shan)(shan)一(yi)(yi)帶(dai),這從五臺山(shan)(shan)(shan)、恒(heng)山(shan)(shan)(shan)山(shan)(shan)(shan)前(qian)發(fa)育(yu)(yu)的(de)(de)(de)串珠(zhu)狀洪積(ji)扇可以(yi)(yi)得到(dao)證明。第四(si)紀(ji)黃(huang)(huang)土(tu)高原(yuan)在抬升的(de)(de)(de)同(tong)時(shi)(shi),邊(bian)緣拗陷(xian)區(qu)如銀川平原(yuan)、汾渭谷(gu)地(di)在大幅度(du)(du)下沉(chen),渭河(he)(he)平原(yuan)固(gu)始凹陷(xian)第四(si)紀(ji)沉(chen)積(ji)物厚度(du)(du)接近1000米。據地(di)形(xing)變形(xing)資料,汾渭地(di)塹的(de)(de)(de)下沈速度(du)(du)為(wei)3毫(hao)米/年(nian)。黃(huang)(huang)河(he)(he)自140萬年(nian)前(qian)后(hou)沖出(chu)三(san)門峽后(hou),汾渭谷(gu)地(di)是黃(huang)(huang)河(he)(he)中(zhong)游眾多支(zhi)流(liu)的(de)(de)(de)侵(qin)蝕(shi)基準面(mian),一(yi)(yi)方(fang)面(mian)黃(huang)(huang)土(tu)高原(yuan)不斷抬升,另一(yi)(yi)方(fang)面(mian)汾渭谷(gu)地(di)持續下沉(chen),必然對(dui)黃(huang)(huang)土(tu)高原(yuan)土(tu)壤(rang)侵(qin)蝕(shi)起促進作用。地(di)震是黃(huang)(huang)土(tu)高原(yuan)新(xin)(xin)構(gou)(gou)造(zao)運(yun)動(dong)的(de)(de)(de)強烈表現形(xing)式,對(dui)歷史(shi)(shi)時(shi)(shi)期黃(huang)(huang)土(tu)高原(yuan)地(di)震記載(zai)進行統計,可以(yi)(yi)反映出(chu)黃(huang)(huang)土(tu)高原(yuan)歷史(shi)(shi)時(shi)(shi)期新(xin)(xin)構(gou)(gou)造(zao)運(yun)動(dong)的(de)(de)(de)強弱變化過程。
黃土高原是中華民(min)族(zu)的發(fa)祥地(di)(di)(di)(di)(di)之一(yi),新石器時(shi)期文化遺址在(zai)黃土高原南(nan)部分布廣泛,尤其在(zai)汾(fen)渭(wei)河(he)谷地(di)(di)(di)(di)(di)和(he)豫(yu)西地(di)(di)(di)(di)(di)區稠(chou)密。當時(shi)人(ren)們以(yi)漁獵(lie)、采集為生(sheng),說明當時(shi)黃土高原南(nan)部維(wei)持(chi)著(zhu)較好的自然生(sheng)態系(xi)統。商周時(shi)期中國出(chu)現了文字記載,生(sheng)產力水(shui)平的提(ti)高,農(nong)(nong)(nong)(nong)業(ye)(ye)生(sheng)產由原始(shi)農(nong)(nong)(nong)(nong)業(ye)(ye)向傳統農(nong)(nong)(nong)(nong)業(ye)(ye)轉(zhuan)變(bian)。商周時(shi)周人(ren)主要活動的北豳(慶陽、西峰一(yi)帶(dai)(dai))、古(gu)豳(彬縣、長武(wu)一(yi)帶(dai)(dai))、周原(扶風、岐山一(yi)帶(dai)(dai))鋤耕(geng)農(nong)(nong)(nong)(nong)業(ye)(ye)已(yi)發(fa)展(zhan)到一(yi)定水(shui)平。夏代(dai)(dai)中國有(you)人(ren)口1355萬,周代(dai)(dai)1371萬人(ren),其中1/2左右分布在(zai)汾(fen)渭(wei)河(he)谷和(he)豫(yu)西地(di)(di)(di)(di)(di)區,這(zhe)兩地(di)(di)(di)(di)(di)區人(ren)口密度30-40人(ren)/平方千米。即便如此,從《詩經》中仍可看(kan)到黃土高原南(nan)部野鹿成群,虎豹出(chu)沒,森林(lin)面(mian)積廣大(da),農(nong)(nong)(nong)(nong)耕(geng)面(mian)積有(you)限(xian)。春秋、戰國時(shi)期鐵(tie)器出(chu)現,犁耕(geng)農(nong)(nong)(nong)(nong)業(ye)(ye)逐漸代(dai)(dai)替鋤耕(geng)農(nong)(nong)(nong)(nong)業(ye)(ye),關中、汾(fen)河(he)谷地(di)(di)(di)(di)(di)、洛陽盆地(di)(di)(di)(di)(di)、天水(shui)盆地(di)(di)(di)(di)(di)農(nong)(nong)(nong)(nong)業(ye)(ye)進一(yi)步發(fa)展(zhan)。戰國時(shi)秦將(jiang)自己(ji)的勢力向渭(wei)河(he)上游(you)、陜北北部推(tui)進,趙則向晉(jin)北地(di)(di)(di)(di)(di)區擴張,在(zai)這(zhe)些地(di)(di)(di)(di)(di)區建(jian)立城邑,開(kai)墾土地(di)(di)(di)(di)(di),發(fa)展(zhan)耕(geng)作,但直(zhi)到戰國末農(nong)(nong)(nong)(nong)耕(geng)業(ye)(ye)主要集中在(zai)太原一(yi)龍門一(yi)天水(shui)以(yi)南(nan)地(di)(di)(di)(di)(di)區,以(yi)北畜牧業(ye)(ye)仍占優(you)勢,整個黃土高原人(ren)口少,開(kai)墾指(zhi)數不高。
秦(qin)漢(han)(han)、隋唐黃(huang)土(tu)高(gao)(gao)原(yuan)(yuan)(yuan)是中(zhong)國(guo)(guo)的(de)(de)政治(zhi)、經濟中(zhong)心,人日與土(tu)地(di)(di)(di)利用變(bian)化較大(da)。秦(qin)統一(yi)全(quan)國(guo)(guo)后(hou)統治(zhi)范圍向(xiang)(xiang)北(bei)(bei)推(tui)進到黃(huang)土(tu)高(gao)(gao)原(yuan)(yuan)(yuan)北(bei)(bei)部秦(qin)長城一(yi)線(xian)(xian)。西(xi)(xi)漢(han)(han)時(shi)期(qi)統治(zhi)范圍進一(yi)步向(xiang)(xiang)北(bei)(bei)、向(xiang)(xiang)西(xi)(xi)推(tui)進,漢(han)(han)武帝(di)時(shi)向(xiang)(xiang)北(bei)(bei)到達陰山(shan),向(xiang)(xiang)西(xi)(xi)到達河西(xi)(xi)走廊,黃(huang)土(tu)高(gao)(gao)原(yuan)(yuan)(yuan)幾乎(hu)全(quan)部都在西(xi)(xi)漢(han)(han)的(de)(de)統治(zhi)之下。秦(qin)漢(han)(han)時(shi)期(qi)是中(zhong)國(guo)(guo)農(nong)(nong)(nong)(nong)業發展(zhan)的(de)(de)高(gao)(gao)峰(feng),農(nong)(nong)(nong)(nong)耕(geng)文(wen)化大(da)舉進入黃(huang)土(tu)高(gao)(gao)原(yuan)(yuan)(yuan),從綏德、米(mi)(mi)脂(zhi)一(yi)帶出土(tu)的(de)(de)漢(han)(han)畫像石可以(yi)(yi)清楚地(di)(di)(di)反映出這一(yi)點。西(xi)(xi)漢(han)(han)時(shi)曾(ceng)向(xiang)(xiang)黃(huang)土(tu)高(gao)(gao)原(yuan)(yuan)(yuan)大(da)量移民,再加上(shang)大(da)批吏卒屯守(shou)邊防,黃(huang)土(tu)高(gao)(gao)原(yuan)(yuan)(yuan)人口(kou)迅速(su)增加。據(ju)《漢(han)(han)書(shu)·地(di)(di)(di)理志(zhi)》記載,西(xi)(xi)漢(han)(han)元(yuan)始二(er)年(2年)黃(huang)土(tu)高(gao)(gao)原(yuan)(yuan)(yuan)地(di)(di)(di)區有人口(kou)880萬(wan)人,其中(zhong)洛(luo)陽(yang)盆地(di)(di)(di)人口(kou)密度(du)高(gao)(gao)為(wei)132人/平(ping)方千(qian)米(mi)(mi),關(guan)(guan)中(zhong)為(wei)30一(yi)90人/平(ping)方千(qian)米(mi)(mi),陜(shan)北(bei)(bei)及晉(jin)西(xi)(xi)北(bei)(bei)為(wei)10一(yi)13人/跑(pao)平(ping)方千(qian)米(mi)(mi),天(tian)水盆地(di)(di)(di)為(wei)10.74人/平(ping)方千(qian)米(mi)(mi)。人口(kou)的(de)(de)增加和農(nong)(nong)(nong)(nong)耕(geng)的(de)(de)發展(zhan)使部分林草地(di)(di)(di)被開墾,但開墾程度(du)較高(gao)(gao)主要在南部的(de)(de)關(guan)(guan)中(zhong)、洛(luo)陽(yang)盆地(di)(di)(di)和天(tian)水盆地(di)(di)(di),當時(shi)農(nong)(nong)(nong)(nong)牧業界線(xian)(xian)在太原(yuan)(yuan)(yuan)一(yi)龍門一(yi)寶雞(ji)一(yi)線(xian)(xian)。此線(xian)(xian)以(yi)(yi)北(bei)(bei)的(de)(de)廣(guang)大(da)黃(huang)土(tu)丘陵地(di)(di)(di)區耕(geng)地(di)(di)(di)主要分布在河谷(gu)平(ping)原(yuan)(yuan)(yuan),其余(yu)地(di)(di)(di)區仍(reng)保持自(zi)然狀態。東(dong)漢(han)(han)、三國(guo)(guo)、兩晉(jin)、十六國(guo)(guo)、南北(bei)(bei)朝(chao)時(shi)期(qi)黃(huang)土(tu)高(gao)(gao)原(yuan)(yuan)(yuan)戰爭頻繁(fan),社會動亂,人口(kou)大(da)量減少(shao),原(yuan)(yuan)(yuan)來的(de)(de)農(nong)(nong)(nong)(nong)耕(geng)區向(xiang)(xiang)南退縮,黃(huang)土(tu)高(gao)(gao)原(yuan)(yuan)(yuan)的(de)(de)廣(guang)大(da)地(di)(di)(di)區重新成為(wei)游(you)牧區,生(sheng)態環境(jing)得以(yi)(yi)恢復。
據《續漢(han)書(shu)·郡國志(zhi)》記載(zai),東(dong)(dong)漢(han)永和五年(140年)黃土(tu)高原(yuan)總(zong)人(ren)(ren)(ren)口(kou)(kou)為(wei)507.6萬(wan)人(ren)(ren)(ren),比西(xi)漢(han)減少了43%。當時(shi)陜(shan)北及晉(jin)(jin)西(xi)北人(ren)(ren)(ren)口(kou)(kou)4.94萬(wan)人(ren)(ren)(ren),比西(xi)漢(han)的(de)130.55萬(wan)人(ren)(ren)(ren)減少96%,人(ren)(ren)(ren)口(kou)(kou)密(mi)度(du)(du)減為(wei)0.5人(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)(fang)千(qian)(qian)(qian)米(mi)(mi)以下。西(xi)晉(jin)(jin)時(shi)黃土(tu)高原(yuan)人(ren)(ren)(ren)口(kou)(kou)比東(dong)(dong)漢(han)又有(you)減少,據《晉(jin)(jin)書(shu)·地理(li)志(zhi)》記載(zai),西(xi)晉(jin)(jin)太康元(yuan)年(280年)黃土(tu)高原(yuan)總(zong)人(ren)(ren)(ren)口(kou)(kou)204萬(wan)人(ren)(ren)(ren),比東(dong)(dong)漢(han)減少4%5。《晉(jin)(jin)書(shu)》中山西(xi)河曲、偏關、保德、陜(shan)北、隴東(dong)(dong)馬連河流域為(wei)游牧民(min)族居住區,無人(ren)(ren)(ren)日記載(zai),人(ren)(ren)(ren)口(kou)(kou)當比東(dong)(dong)漢(han)時(shi)更為(wei)稀疏(shu)。當時(shi)西(xi)安附(fu)近的(de)京(jing)兆人(ren)(ren)(ren)口(kou)(kou)密(mi)度(du)(du)為(wei)34.88人(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)(fang)千(qian)(qian)(qian)米(mi)(mi),關中東(dong)(dong)部(bu)的(de)左馮詡為(wei)3.29人(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)(fang)千(qian)(qian)(qian)米(mi)(mi),關中西(xi)部(bu)的(de)右扶風為(wei)9.46人(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)(fang)千(qian)(qian)(qian)米(mi)(mi),洛陽附(fu)近為(wei)55.85人(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)(fang)千(qian)(qian)(qian)米(mi)(mi),天水附(fu)近為(wei)5.55人(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)(fang)千(qian)(qian)(qian)k/耐,比西(xi)漢(han)時(shi)減少l2/以上(shang)。
隋(sui)唐(tang)(tang)時(shi)中(zhong)國重(zhong)新歸于統一(yi),而且(qie)社會安定,經(jing)濟(ji)繁榮,成為中(zhong)國農(nong)業(ye)發展的(de)第二(er)個鼎(ding)盛時(shi)期。隨著經(jing)濟(ji)的(de)發展,黃(huang)土(tu)(tu)高原(yuan)(yuan)(yuan)人(ren)(ren)(ren)口增(zeng)加,農(nong)耕(geng)業(ye)逐步(bu)代替游牧業(ye)。《隋(sui)書·地(di)理志》記載,隋(sui)大業(ye)五年(nian)(nian)(609年(nian)(nian))黃(huang)土(tu)(tu)高原(yuan)(yuan)(yuan)總(zong)人(ren)(ren)(ren)口為1104萬(wan)人(ren)(ren)(ren),是西(xi)漢(han)的(de)125%、西(xi)晉的(de)5.14倍(bei)。陜北、晉西(xi)北人(ren)(ren)(ren)口密度(du)己經(jing)趕上了西(xi)漢(han),徑河(he)上游、馬連河(he)上游己是西(xi)漢(han)的(de)數倍(bei),唐(tang)(tang)初實(shi)行均田制,關中(zhong)大興(xing)水(shui)利,不僅使(shi)關中(zhong)、汾(fen)河(he)下游,洛陽盆地(di)全部(bu)成為農(nong)業(ye)區(qu),而且(qie)農(nong)耕(geng)業(ye)擴大到地(di)勢較高的(de)黃(huang)上臺源、北山南麓(lu)黃(huang)土(tu)(tu)覆蓋的(de)山前平源。農(nong)耕(geng)區(qu)還沿渭河(he)向西(xi)到達天水(shui)、隴(long)西(xi),直(zhi)至涅水(shui)湟水(shui)河(he)谷地(di)。天寶時(shi)(742一(yi)755年(nian)(nian))唐(tang)(tang)代經(jing)濟(ji)達到了頂峰,當時(shi)黃(huang)土(tu)(tu)高原(yuan)(yuan)(yuan)人(ren)(ren)(ren)口1015萬(wan)人(ren)(ren)(ren),關中(zhong)、汾(fen)河(he)下游、洛陽盆地(di)人(ren)(ren)(ren)口密度(du)50-100人(ren)(ren)(ren)/平方千米。隋(sui)唐(tang)(tang)時(shi)期基本奠(dian)定了黃(huang)上高原(yuan)(yuan)(yuan)南部(bu)農(nong)業(ye)生產的(de)格局,人(ren)(ren)(ren)口增(zeng)加,植被破壞,城(cheng)鎮興(xing)起(qi),對這一(yi)地(di)區(qu)土(tu)(tu)壤侵(qin)蝕產生了明顯的(de)影響。但黃(huang)土(tu)(tu)高原(yuan)(yuan)(yuan)中(zhong)部(bu)、北部(bu)自然環境的(de)總(zong)體破壞程(cheng)度(du)并不甚嚴重(zhong),黃(huang)土(tu)(tu)丘陵地(di)區(qu)畜牧業(ye)仍占較大比重(zhong)。
唐以后的五(wu)代(dai)(dai)(dai)十(shi)國(907一(yi)979年)黃(huang)土(tu)(tu)(tu)高原(yuan)(yuan)人(ren)(ren)(ren)口有(you)較(jiao)大(da)(da)幅度(du)(du)減少,但到宋(song)代(dai)(dai)(dai)人(ren)(ren)(ren)口得到恢復。據研究(jiu)南(nan)宋(song)嘉定(ding)三年(1210年)山西(xi)人(ren)(ren)(ren)口密度(du)(du)為(wei)45.72人(ren)(ren)(ren)/平(ping)方(fang)(fang)千(qian)(qian)(qian)米(mi)(mi),陜(shan)西(xi)為(wei)21.44人(ren)(ren)(ren)/平(ping)方(fang)(fang)千(qian)(qian)(qian)米(mi)(mi)。北宋(song)在黃(huang)上(shang)高原(yuan)(yuan)上(shang)形成一(yi)條與遼、西(xi)夏對(dui)峙的軍事分界(jie)線(xian)(xian),這條界(jie)線(xian)(xian)東(dong)起(qi)大(da)(da)同(tong)以南(nan),經陜(shan)北、寧(ning)夏南(nan)部(bu)、蘭(lan)州以北直至(zhi)西(xi)寧(ning)以西(xi),綿延1000千(qian)(qian)(qian)米(mi)(mi)。沿(yan)這條分界(jie)線(xian)(xian),北宋(song)修筑(zhu)了(le)大(da)(da)量(liang)城鎮(zhen)、堡寨、派駐大(da)(da)批軍隊戍邊防衛。為(wei)解(jie)決(jue)軍隊給養,招募人(ren)(ren)(ren)口沿(yan)邊屯耕,沿(yan)分界(jie)線(xian)(xian)形成了(le)一(yi)條人(ren)(ren)(ren)口稠密,墾殖程度(du)(du)較(jiao)高的地帶,也使此(ci)分界(jie)線(xian)(xian)所經地區生態嚴重惡(e)化。此(ci)線(xian)(xian)以南(nan)的黃(huang)土(tu)(tu)(tu)丘陵(ling)溝(gou)壑區仍然以牧為(wei)主,與唐代(dai)(dai)(dai)后期比較(jiao),土(tu)(tu)(tu)地利(li)用沒(mei)有(you)太大(da)(da)變化。元(yuan)代(dai)(dai)(dai)統一(yi)后,黃(huang)上(shang)高原(yuan)(yuan)雖結(jie)束了(le)軍事對(dui)壘(lei),但元(yuan)代(dai)(dai)(dai)連年殘酷(ku)的戰(zhan)爭(zheng)和元(yuan)對(dui)漢(han)人(ren)(ren)(ren)實(shi)行的屠殺政策,黃(huang)土(tu)(tu)(tu)高原(yuan)(yuan)人(ren)(ren)(ren)口大(da)(da)幅減少,元(yuan)至(zhi)元(yuan)二十(shi)七年(1290年)山西(xi)人(ren)(ren)(ren)口密度(du)(du)僅為(wei)8.20人(ren)(ren)(ren)/平(ping)方(fang)(fang)千(qian)(qian)(qian)米(mi)(mi),陜(shan)西(xi)2.57人(ren)(ren)(ren)/平(ping)方(fang)(fang)千(qian)(qian)(qian)米(mi)(mi),寧(ning)夏2.82人(ren)(ren)(ren)/平(ping)方(fang)(fang)千(qian)(qian)(qian)米(mi)(mi),甘肅2.15人(ren)(ren)(ren)/平(ping)方(fang)(fang)千(qian)(qian)(qian)米(mi)(mi)。
明代黃土(tu)(tu)高原人(ren)(ren)(ren)(ren)(ren)(ren)(ren)口(kou)(kou)得到(dao)恢復,明弘(hong)治四年(nian)(nian)(1491年(nian)(nian))山(shan)西人(ren)(ren)(ren)(ren)(ren)(ren)(ren)口(kou)(kou)密度(du)(du)達到(dao)31.6人(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)千(qian)(qian)(qian)(qian)米(mi)(mi),陜(shan)西15.68人(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)千(qian)(qian)(qian)(qian)米(mi)(mi),寧(ning)夏5.02人(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)千(qian)(qian)(qian)(qian)米(mi)(mi),,甘肅4.41人(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)千(qian)(qian)(qian)(qian)米(mi)(mi),青海1.45人(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)千(qian)(qian)(qian)(qian)米(mi)(mi)。明自(zi)建國之初就在(zai)黃土(tu)(tu)高原北部修筑長(chang)(chang)城(cheng)(cheng)(cheng)(cheng)(cheng),在(zai)修建長(chang)(chang)城(cheng)(cheng)(cheng)(cheng)(cheng)的(de)同時,沿長(chang)(chang)城(cheng)(cheng)(cheng)(cheng)(cheng)大興城(cheng)(cheng)(cheng)(cheng)(cheng)鎮聚(ju)落,移民實邊(bian),長(chang)(chang)城(cheng)(cheng)(cheng)(cheng)(cheng)沿線(xian)形成(cheng)人(ren)(ren)(ren)(ren)(ren)(ren)(ren)口(kou)(kou)密集的(de)地帶(dai),其人(ren)(ren)(ren)(ren)(ren)(ren)(ren)口(kou)(kou)遠較長(chang)(chang)城(cheng)(cheng)(cheng)(cheng)(cheng)以(yi)南的(de)黃土(tu)(tu)丘陵溝(gou)壑區稠(chou)密。如嘉慶《重修一統志》記載,嘉慶二十五年(nian)(nian)(1820年(nian)(nian))山(shan)西寧(ning)武人(ren)(ren)(ren)(ren)(ren)(ren)(ren)口(kou)(kou)密度(du)(du)為(wei)40.26人(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)千(qian)(qian)(qian)(qian)米(mi)(mi),保德(de)為(wei)50.64人(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)千(qian)(qian)(qian)(qian)米(mi)(mi),而(er)其南部的(de)爆州僅22.88人(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)千(qian)(qian)(qian)(qian)米(mi)(mi);榆林人(ren)(ren)(ren)(ren)(ren)(ren)(ren)口(kou)(kou)密度(du)(du)41.99人(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)千(qian)(qian)(qian)(qian)米(mi)(mi),而(er)其南部的(de)綏德(de)僅33.17人(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)千(qian)(qian)(qian)(qian)米(mi)(mi),延(yan)安僅19.58人(ren)(ren)(ren)(ren)(ren)(ren)(ren)/平(ping)(ping)方(fang)(fang)千(qian)(qian)(qian)(qian)米(mi)(mi),。當(dang)時的(de)長(chang)(chang)城(cheng)(cheng)(cheng)(cheng)(cheng)是農(nong)牧業的(de)分(fen)界(jie)線(xian),長(chang)(chang)城(cheng)(cheng)(cheng)(cheng)(cheng)沿線(xian)不(bu)僅分(fen)布著數百(bai)萬邊(bian)民,而(er)且駐軍也三(san)分(fen)戍(shu)守,七分(fen)屯田,每個屯田士卒須種地50畝(mu),使長(chang)(chang)城(cheng)(cheng)(cheng)(cheng)(cheng)沿線(xian)被徹(che)底開墾(ken),長(chang)(chang)城(cheng)(cheng)(cheng)(cheng)(cheng)以(yi)南則農(nong)牧業兼有。
清(qing)代(dai)國家(jia)統一(yi),社會安(an)定,人(ren)口增長快。明弘治四年(1491年)黃(huang)(huang)土(tu)高(gao)原(yuan)總人(ren)口達到1500萬人(ren)。經200多年到嘉(jia)慶二十五年(1820年)人(ren)口達到1995萬。到道光二十年(1840年)人(ren)口增至4100萬人(ren),達到封建(jian)時代(dai)黃(huang)(huang)土(tu)高(gao)原(yuan)人(ren)口的(de)(de)峰值。1820年黃(huang)(huang)土(tu)高(gao)原(yuan)人(ren)口密度是:山(shan)西91.36人(ren)/平(ping)(ping)(ping)方(fang)(fang)(fang)(fang)千(qian)(qian)米,陜西61.16人(ren)/平(ping)(ping)(ping)方(fang)(fang)(fang)(fang)千(qian)(qian)米,甘肅(su)34.24人(ren)/平(ping)(ping)(ping)方(fang)(fang)(fang)(fang)千(qian)(qian)米,寧(ning)夏31.37人(ren)/平(ping)(ping)(ping)方(fang)(fang)(fang)(fang)千(qian)(qian)米,青海6.95人(ren)/平(ping)(ping)(ping)方(fang)(fang)(fang)(fang)千(qian)(qian)米。其(qi)中(zhong)關中(zhong)、諫(jian)汾河谷地(di),洛陽盆地(di)達100-200人(ren)/平(ping)(ping)(ping)方(fang)(fang)(fang)(fang)千(qian)(qian)米,晉西北、陜北、隴東達40-80人(ren)/平(ping)(ping)(ping)方(fang)(fang)(fang)(fang)千(qian)(qian)米,如(ru)平(ping)(ping)(ping)涼82.62人(ren)/平(ping)(ping)(ping)方(fang)(fang)(fang)(fang)千(qian)(qian)米,慶陽57.33人(ren)/平(ping)(ping)(ping)方(fang)(fang)(fang)(fang)千(qian)(qian)米,徑陽101.61人(ren)/平(ping)(ping)(ping)方(fang)(fang)(fang)(fang)千(qian)(qian)米。明清(qing)時期(qi)長城以南的(de)(de)疏林灌叢已(yi)被連(lian)片開墾。另一(yi)方(fang)(fang)(fang)(fang)面(mian)由于人(ren)地(di)矛(mao)盾加劇,清(qing)末(mo)移入(ru)黃(huang)(huang)土(tu)高(gao)原(yuan)的(de)(de)移民(min)向人(ren)煙少的(de)(de)山(shan)區(qu)遷移,如(ru)寧(ning)夏南部地(di)區(qu)、呂梁山(shan)西側、黃(huang)(huang)龍山(shan)區(qu)等(deng),使這些原(yuan)來的(de)(de)林區(qu)也逐步(bu)轉變為農耕區(qu)。可以說(shuo)明清(qing)時期(qi)黃(huang)(huang)土(tu)高(gao)原(yuan)丘陵溝壑區(qu)徹(che)底(di)演變成了農耕區(qu)。
20世紀前半葉由于(yu)戰亂和自(zi)然(ran)災(zai)害,黃土(tu)(tu)高(gao)原(yuan)人(ren)(ren)口(kou)有所減(jian)少(shao),1935年(nian)(nian)總(zong)人(ren)(ren)口(kou)為2960萬(wan)(wan)(wan)人(ren)(ren),1949年(nian)(nian)為3936萬(wan)(wan)(wan)人(ren)(ren),人(ren)(ren)口(kou)分布和清末沒有大的(de)(de)不(bu)同(tong)。建(jian)國(guo)后,黃土(tu)(tu)高(gao)原(yuan)人(ren)(ren)口(kou)增長(chang)極快(kuai)(kuai),70年(nian)(nian)代以(yi)前平(ping)(ping)均人(ren)(ren)口(kou)增長(chang)速度35.3‰。遠(yuan)高(gao)于(yu)中(zhong)國(guo)的(de)(de)21.2‰的(de)(de)水(shui)(shui)平(ping)(ping);70年(nian)(nian)代以(yi)后人(ren)(ren)口(kou)增長(chang)速度14.6-21.0‰,仍高(gao)于(yu)中(zhong)國(guo)平(ping)(ping)均水(shui)(shui)平(ping)(ping),是中(zhong)國(guo)人(ren)(ren)口(kou)增長(chang)快(kuai)(kuai)的(de)(de)地(di)區(qu)之一。1960年(nian)(nian)總(zong)人(ren)(ren)口(kou)達到(dao)4913.4萬(wan)(wan)(wan)人(ren)(ren),1980年(nian)(nian)達到(dao)7521.萬(wan)(wan)(wan)人(ren)(ren),1990年(nian)(nian)達到(dao)9031萬(wan)(wan)(wan)人(ren)(ren),人(ren)(ren)口(kou)的(de)(de)增加使耕(geng)地(di)面積(ji)不(bu)斷(duan)增加,林(lin)地(di)、草地(di)面積(ji)減(jian)少(shao)。1949-1985年(nian)(nian)黃土(tu)(tu)高(gao)原(yuan)耕(geng)地(di)增加393.3x10000平(ping)(ping)方百米(mi),增長(chang)率(lv)為30.6%。耕(geng)地(di)增加主要(yao)集(ji)中(zhong)在水(shui)(shui)土(tu)(tu)流失嚴重的(de)(de)黃土(tu)(tu)丘(qiu)陵地(di)區(qu),凈增耕(geng)地(di)272x10000平(ping)(ping)方百米(mi),占黃土(tu)(tu)高(gao)原(yuan)凈增耕(geng)地(di)的(de)(de)69%,使這(zhe)些地(di)區(qu)陷(xian)入“越窮越墾,越墾越窮”的(de)(de)經濟(ji)、生(sheng)態雙(shuang)重貧困。
中(zhong)國(guo)實(shi)行改革開放以后,黃土(tu)高(gao)原地(di)(di)區的(de)(de)(de)國(guo)內(nei)生產(chan)總(zong)值總(zong)量呈(cheng)現(xian)持續的(de)(de)(de)增長態勢。西部大(da)開發(fa)戰略的(de)(de)(de)實(shi)施成為(wei)該地(di)(di)區2000年以后國(guo)內(nei)生產(chan)總(zong)值占中(zhong)國(guo)比重(zhong)迅速提高(gao)的(de)(de)(de)主(zhu)要(yao)誘因(yin),而晉(jin)陜蒙(meng)地(di)(di)區能(neng)礦(kuang)產(chan)資(zi)源的(de)(de)(de)開發(fa)則是(shi)其直接動(dong)(dong)因(yin)。黃土(tu)高(gao)原地(di)(di)區人均(jun)國(guo)內(nei)生產(chan)總(zong)值的(de)(de)(de)空間分(fen)布(bu)(bu)整體上呈(cheng)現(xian)出“兩高(gao)一低(di)”的(de)(de)(de)帶(dai)狀分(fen)布(bu)(bu)格(ge)(ge)局(ju)(ju),且這種空間分(fen)布(bu)(bu)格(ge)(ge)局(ju)(ju)明(ming)顯地(di)(di)隨著時間受到極(ji)化增長的(de)(de)(de)擾動(dong)(dong)和(he)重(zhong)塑。能(neng)礦(kuang)資(zi)源開發(fa)、農(nong)業密(mi)集(ji)程(cheng)度、人口(kou)分(fen)布(bu)(bu)狀況和(he)自然本底條件等是(shi)影(ying)響(xiang)該地(di)(di)區人均(jun)國(guo)內(nei)生產(chan)總(zong)值空間分(fen)布(bu)(bu)格(ge)(ge)局(ju)(ju)及其變動(dong)(dong)關鍵的(de)(de)(de)因(yin)素(su)。